Host attestation

ABSTRACT

A service provider provides virtual computing services using a fleet of one or more host computer systems. Each of the host computer systems may be equipped with a trusted platform module (“TPM”). The service provider, the host computer systems, and the virtual computing environments generate attestations that prove the integrity of the system. The attestations are signed with a one-time-use cryptographic key that is verifiable against the public keys of the service provider, a host computer system, and a virtual computing environment. The public key of the host computer system is integrated into a hash tree that links the public key of the host computer system to the public key of the service provider. The public key of the virtual computing environment is signed using a one-time-use graphic key issued to the host computer system that hosts the virtual computing environment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 16/298,867, filed on Mar. 11, 2019, entitled “HOST ATTESTATION,” which is a divisional of U.S. patent application Ser. No. 15/389,771, filed on Dec. 23, 2016, now U.S. Pat. No. 10,229,270, entitled “HOST ATTESTATION,” which is incorporated herein by reference for all purposes.

This application incorporates by reference for all purposes the full disclosures of co-pending U.S. patent application Ser. No. 15/390,176, filed Dec. 23, 2016, now U.S. Pat. No. 10,218,511, entitled “SIGNATURE DELEGATION,” co-pending U.S. patent application Ser. No. 15/946,614, filed Apr. 5, 2018, now U.S. Pat. No. 10,129,034, entitled “SIGNATURE DELEGATION,” co-pending U.S. patent application Ser. No. 15/389,686, filed Dec. 23, 2016, now U.S. Pat. No. 10,230,525, entitled “PUBLIC KEY ROLLUP FOR MERKLE TREE SIGNATURE SCHEME,” co-pending U.S. patent application Ser. No. 15/390,205, filed Dec. 23, 2016, now U.S. Pat. No. 10,237,249, entitled “KEY REVOCATION,” and co-pending U.S. patent application Ser. No. 15/390,214, filed Dec. 23, 2016, now U.S. Pat. No. 10,243,939, entitled “KEY DISTRIBUTION INA DISTRIBUTED COMPUTING ENVIRONMENT.”

BACKGROUND

For many businesses, third-party computing resource service providers are an important part of their computing infrastructure. Many businesses deploy application programs to virtual computing environments provided by third-party computing resource service providers. As the resource demands of a particular application change over time, business administrators are able to scale each virtual computing environment up or down as needed. However, when using virtual computing environments in this way, it is important for the user of the virtual computing environment to be able to confirm that the computing environment complies with an appropriate configuration. For example, before deploying an application or interacting with a service hosted on a virtual computer system, a customer may desire proof that the virtual computer instance is configured with an authentic image, that the host of the virtual computer instance is properly configured, and that the host of the virtual computer instance is owned by the computing resource service provider.

Protecting the integrity of digital signatures and encrypted communications is an important problem. Many digital signatures and encrypted communications rely on cryptographic keys that are controlled by a central authority. The central authority maintains control over the cryptographic keys which are used to generate digital signatures and perform other cryptographic operations. If the central authority operates as part of a distributed computing environment, cryptographic operations may be performed by a variety of computing entities on behalf of the central authority. In such situations, the various computing entities acting on behalf of the central authority may apply digital signatures or establish cryptographically protected communication sessions using a cryptographic key associated with the central authority. Therefore, controlling the distribution of cryptographic keys from the central authority to the various computing entities that act on the behalf of the central authority is an important problem.

After the cryptographic keys are distributed or used it is sometimes desired to revoke a particular cryptographic key. In such situations, entities verifying a digital signature or the validity of a particular cryptographic key contact a key-revocation authority to inquire whether an associated cryptographic key is revoked or not. For a particular key generation and distribution scheme, it is important for the central authority, or delegate acting on behalf of the central authority, to be able to provide a provable indication that a particular cryptographic key is revoked.

BRIEF DESCRIPTION OF THE DRAWINGS

Various techniques will be described with reference to the drawings, in which:

FIG. 1 shows an illustrative example of an environment in which various embodiments may be practiced;

FIG. 2 shows an illustrative example of a computer system that manages host computer systems for a service provider;

FIG. 3 shows an illustrative example of a host computer system with a trusted platform module (“TPM”) that hosts one or more virtual computer system instances;

FIG. 4 shows an illustrative example of a virtual computer system instance that is able to provide signed attestations of the computing environment;

FIG. 5 shows an illustrative example of a process that, as a result of being performed by a service provider, a host computer system, and a virtual computer system instance, generates and distributes a set of one-time-use cryptographic keys that are used by the virtual client computer system;

FIG. 6 shows an illustrative example of a process that, as a result of being performed by a client application and a virtual computer system instance, generates a signed attestation in response to a request from the client application;

FIG. 7 shows an illustrative example of a process that, as a result of being performed by a client application, verifies a signed attestation provided by a virtual client computer system;

FIG. 8 shows an illustrative example of a one-time-use cryptographic key that includes secret key pairs and corresponding public key pairs;

FIG. 9 shows an illustrative example of signing a message with a one-time-use cryptographic key;

FIG. 10 shows an illustrative example of verifying a message with a one-time-use cryptographic key;

FIG. 11 shows an illustrative example of a secret key with an associated public key;

FIG. 12 shows an illustrative example of a Merkle tree of one-time-use cryptographic keys;

FIG. 13 shows an illustrative example of a number of linked Merkle trees that implement a cryptographic signature scheme for signing attestations;

FIG. 14 shows an illustrative example of an environment in which various embodiments may be practiced;

FIG. 15 shows an illustrative example of a one-time-use cryptographic key that includes secret key pairs and corresponding public key pairs;

FIG. 16 shows an illustrative example of signing a message with a one-time-use cryptographic key;

FIG. 17 shows an illustrative example of verifying a message with a one-time-use cryptographic key;

FIG. 18 shows an illustrative example of a secret key with an associated public key, and a revocation key with an associated revocation hash value;

FIG. 19 shows an illustrative example of a secret key with an associated revocation key that may be used to revoke the signature authority of the secret key;

FIG. 20 shows an illustrative example of a Merkle tree of one-time-use cryptographic keys;

FIG. 21 shows an illustrative example of a Merkle tree of one-time-use cryptographic keys that includes revocation keys for revoking portions of the tree;

FIG. 22 shows an illustrative example of a set of seed values that are used to generate a set of one-time-use keys and corresponding public keys;

FIG. 23 shows an illustrative example of a set of one-time-use cryptographic keys that are generated from a tree of seed values;

FIG. 24 shows an illustrative example of a process that, as a result of being performed by a signature authority, generates a seed tree that supports delegation of one-time-use cryptographic keys;

FIG. 25 shows an illustrative example of a process that, as a result of being performed by a signature authority, delegates a portion of one-time-use cryptographic keys to an authorized entity;

FIG. 26 shows an illustrative example of a process that, as a result of being performed by an authorized entity, signs a message using a one-time-use cryptographic key provided by a signature authority;

FIG. 27 shows an illustrative example of a delegation service that allocates and distributes blocks of cryptographic keys to one or more authorized delegates;

FIG. 28 shows an illustrative example of a process that, as a result of being performed by a key distribution service and a delegate, allocates a block of keys managed by the distribution service to be used by the delegate;

FIG. 29 shows an illustrative example of a process that, as a result of being performed by a signature authority and a delegated key generator, generates a subset of one-time-use keys specified by the signature authority using an intermediate seed value; and

FIG. 30 illustrates an environment in which various embodiments can be implemented.

DETAILED DESCRIPTION

The current document describes a system that produces signed attestations as evidence of the integrity of a virtual computing environment. In various examples, a service provider provides virtual computing services to a customer in the form of one or more virtual computing environments hosted by one or more hosts operated by the service provider. The virtual computing environment may be a virtual machine, container runtime, on-demand execution engine, or other application-execution environment. The service provider may host the virtual computing environments on one or more server computer systems, server clusters, virtual computer systems, or other host computer systems. In order to confirm the trustworthiness and integrity of the virtual computing environments provided, the customer may impose various constraints on the host computer systems used as well as the images installed on the virtual computing environments. In order to confirm that the constraints are complied with, the customer may request an attestation from the service provider, the host computer system, and the virtual computing environment.

The attestation may be generated and signed by a combination of the service provider, the host computer system, and a virtual computing environment. In some examples, the service provider confirms the identity and configuration of the host computer systems, the host computer system confirms the integrity of the host operating environment and the virtual runtime, and the virtual computing environment verifies the configuration of the customer's image. The resulting attestation may be signed using a digital signature that is verifiable using public keys of one or more of the three attesting entities.

In some examples, the service provider uses remote attestation to verify the integrity of host computer systems using a trusted platform module (“TPM”). A signature authority computer system operated by the service provider contacts each host computer system operated by the service provider and requests a signature of various hardware and software installed on the host computer system. A TPM on each host computer system examines the host and generates the requested signature that represents the hardware and software configuration. The TPM signs the signature with a secret portion of an attestation identity key owned by the TPM. In various examples, the attestation identity key is a digital certificate issued by a trusted certificate authority (“CA”), an RSA public-private key pair, or a Merkle signature tree under the control of the TPM. The signature authority computer system receives the signatures from the host computer systems and compares the signatures to reference signatures in a database maintained by the service provider. The host computer systems whose signatures match a valid reference signature in the database are determined by the service provider to be properly configured.

A Merkle tree of one-time-use cryptographic keys is generated for each of the properly configured host computer systems. In some examples, the Merkle trees are generated by the service provider and provided to each host computer system. In another example, the Merkle trees are generated by a TPM on each host and are stored within the TPM on each host. The root node of each Merkle tree acts as a public key for a corresponding individual host computer system. The public keys corresponding to the host computer systems are provided to the signature authority computer system, and the signature authority computer system generates, for the service provider, a Merkle tree of the public keys. The root of the service provider's Merkle tree acts as a public key for the service provider and is published by the signature authority computer system.

As described above, each properly configured host computer system is provided with a Merkle tree of one-time-use cryptographic keys by the service provider. In some examples, the virtual client manager on the host computer system uses the provided one-time-use cryptographic keys to perform additional attestations. In some examples, the attestations may be used to confirm the integrity of the host operating system and/or the virtual runtime. The virtual client manager uses the TPM on the host computer system to generate a host-describing signature describing the configuration of the host operating environment and virtual runtime. The TPM signs the host-describing signature with the attestation identity key, and provides the signed signature to a virtual client manager running on the host computer system. The virtual client manager confirms the signature of the TPM using a public portion of the attestation identity key, and compares the host-describing signature to a set of approved signatures maintained in a host signature database. In other examples, the virtual client manager provides signed code to the TPM, and the TPM executes the signed code to confirm that the host computer system is configured in accordance with customer requirements.

When a virtual client manager on a properly configured host computer system generates a new virtual computing environment, the virtual client manager provides the new virtual computing environment with a set of one-time-use cryptographic keys arranged in a Merkle tree, and the virtual client manager signs the root of the Merkle tree with one of the one-time-use keys provided to the virtual client manager by the service provider. In some implementations, the virtual client manager provides a virtual client manager on the virtual computing environment with the corresponding Merkle tree. In other implementations, the virtual client manager causes the TPM to generate and retain the Merkle trees, and the virtual client manager grants each virtual computing environment access to a Merkle tree by providing each virtual computing environment with access credentials to the TPM. In some examples, before signing the root of the Merkle tree, the virtual client manager confirms the integrity of the virtual computing environment. For example, the virtual client manager may use the TPM to generate a signature of the image of the virtual computing environment or portion of the virtual computing environment, and compare the signature against a database of approved image signatures. The signed root of the Merkle tree provided to the virtual computing environment becomes the public key of the virtual computing environment.

Using the provided signed Merkle tree of one-time-use cryptographic keys, a virtual client manager in the virtual computing environment is able to produce signed attestations for customer applications, end users, and other entities regarding the integrity of the virtual computing environment. In one example, a customer service is deployed to a virtual computing environment, and the customer service requests, from the virtual client manager running within the virtual computing environment, an attestation that the virtual computing environment is a properly configured environment hosted by the service provider. The virtual client manager verifies various environment properties as requested by the customer service (possibly using the TPM) and, using the credentials provided by the host computer system, accesses the Merkle tree of one-time-use keys provided by the host computer system when the virtual computing environment was created. An unused one-time-use key is selected from the Merkle tree and used to sign the attestation. The signed attestation is provided to the customer service.

The customer, end user, or client application may use the signed attestation to verify the state of the service provider, the host computer system, and the virtual computing environment. The signature on the attestation is confirmed by verifying the signature using the public keys associated with the virtual computing environment. The root of the Merkle tree of the virtual computing environment is signed by the host computer system. The signature of the root of the Merkle tree of the virtual computing environment is verified against a public key of the host computer system. The public key of the host computer system is a leaf node of the Merkle tree of the service provider and is verified against the public key of the service provider.

The current document describes methods of generating, distributing, and revoking one-time-use cryptographic keys. One-time-use cryptographic keys may be generated and used as part of a Lamport signature scheme, Winternitz signature scheme, or other cryptographic one-time signature scheme. Each one-time-use cryptographic key includes a secret key and an associated public key or hash value. A signature authority pre-generates a collection of one-time-use cryptographic keys that is used for generating digital signatures. The collection of one-time-use cryptographic keys is generated from a secret seed value, or in some implementations, a set of related seed values, using a key-derivation method. The collection of one-time-use cryptographic keys is arranged in a Merkle tree, and hash values associated with the one-time-use cryptographic keys are used to cryptographically derive a root node of the Merkle tree which serves as a public key for the signature authority.

In some examples, the set of seed values is arranged in a tree structure that corresponds to the structure of the Merkle tree. A master seed value corresponding to the root node of the Merkle tree is used to generate a seed value for each child node of the root node using a one-way function. The seed value associated with each intermediate node is used to generate seed values for each child node. Seed values associated with leaf nodes are used to generate cryptographic keys using a key derivation function.

The signature authority is able to delegate signature authority to a delegate computing entity by providing a portion of the cryptographic keys to the delegate. The signature authority provides a subset of the cryptographic keys to the delegate by providing a seed value corresponding to a node of the Merkle tree to the delegate. Using the seed value, the delegate is able to generate the set of cryptographic keys that are children of the corresponding node of the Merkle tree. In addition to the seed value, the signature authority provides supporting information to the delegate. The supporting information includes the location of the seed value within the Merkle tree, the depth, fanout, and number of cryptographic keys in the Merkle tree, and intermediate hash values in the Merkle tree that are used to verify signatures generated using the delegated cryptographic keys.

When a requester submits a signing request to the delegate, the delegate computing entity generates a digital signature on behalf of the signature authority by selecting a cryptographic key pair that has not yet been used from the delegated set of keys, and generates a digital signature for a message provided by the requester. The delegate provides the requester with the signature, the hashes of the cryptographic key pair, and the hashes associated with intermediate and adjacent nodes of the Merkle tree up to the root node of the signature authority. After producing the digital signature, the delegate marks the selected cryptographic key pair as having been used to generate a digital signature. In many implementations, the selected cryptographic key pair is used once and not reused. If the selected cryptographic key pair is reused, the cryptographic security of the digital signature is greatly reduced with each successive use.

A recipient of the digital signature validates the digital signature by calculating the hash value of the signature, confirming that the hash value matches the appropriate portions of the hashes corresponding to the cryptographic key pair, and confirming the hashes of the cryptographic key pair by verifying the hashes of the intermediate Merkle tree nodes up to the root of the signature authority. If any of the checks fail, the digital signature is not valid.

In some examples, the signature authority retains an ability to revoke a digital signature or invalidate a particular cryptographic key. To provide for revocation of a particular cryptographic key, the signature authority determines a secret revocation value and a hash of the secret revocation value. The hash of the secret revocation value (revocation hash), is hashed together with the hash of a particular cryptographic key to produce a leaf-node hash of a Merkle tree. The revocation hash is published with the hash of the secret cryptographic key to enable verification of signatures created with the secret cryptographic key. To revoke the particular cryptographic key, the signature authority publishes the secret revocation value. When a recipient of the digital signature attempts to confirm the validity of the particular cryptographic key, the signature authority indicates that the particular cryptographic key is revoked and provides the secret revocation value as proof that the signature authority is the owner of the particular cryptographic key. The recipient of the digital signature can confirm the secret revocation value by confirming that the hash of the secret revocation value matches the published revocation hash, and that the hashes of the Merkle tree roll up to the published public key. In some implementations, the signature authority provides secret revocation values for non-leaf nodes of the Merkle tree. By publishing a secret revocation value of a non-leaf node, the signature authority may revoke cryptographic keys and associated digital signatures that are children of the non-leaf node within the Merkle tree.

In some examples, the signature authority provides a key-distribution service that distributes blocks of cryptographic keys to authorized signing delegates. An authorized signing delegate contacts the key-distribution service and requests a block of cryptographic keys. The number of cryptographic keys requested by a particular delegate is based at least in part on a predicted volume of digital signatures to be produced by the particular delegate. If the delegate performing digital signatures on behalf of the signature authority runs out of keys, the signature authority may allocate additional cryptographic keys to the delegate via the key-distribution service. The signature authority maintains a record of which keys have been distributed and used. In some implementations, the signature authority monitors the digital signatures produced by signing delegates to ensure that cryptographic keys are not reused.

FIG. 1 shows an illustrative example of an environment in which various embodiments may be practiced. A diagram 100 shows a system where signed attestations establish the integrity of a virtual computing environment. A service provider provides computing services to customers via a fleet of computer systems, storage systems, and other computing infrastructure. A service provider computer system 102 maintains a service provider key store 104. The service provider key store retains cryptographic information including cryptographic keys, hashes, and digital certificates controlled by the service provider.

The service provider maintains a fleet of host computer systems that includes a host computer system 106. The host computer system 106 is used to provide virtual computing environments to customers of the service provider. In some examples, the host computer system 106 is used to provide virtual machines to customers. In another example, the host computer system is used to provide an on-demand function execution service. In yet another example, the host computer system is used to host a container runtime that hosts containerized applications provided by customers. The host computer system 106 maintains a host key store 108 that retains cryptographic keys, hashes, digital certificates, or other cryptographic information associated with the host computer system 106. In some implementations, the host computer system 106 includes a trusted platform module (“TPM”) and the host key store 108 resides within the TPM. In another implementation, the host computer system 106 retains the host key store 108 and a memory outside the TPM, and the TPM applies a signature to the host key store 108.

The host computer system 106 hosts one or more virtual computing environments including the virtual computer system 110. The virtual computer system 110 is a virtual machine generated by the host computer system 106 and may be loaded with a customer image by the host computer system 106. The virtual computer system 110 accesses a VM key store 112. The VM key store may be retained in memory associated with the virtual computer system 110 or within a TPM on the host computer system 106. The virtual computer system 110 includes an attestation service that may be accessed by applications, end users, or other entities. The attestation service provides signed attestations that the virtual computer system 110, the host computer system 106, and the service provider computer system 102 are properly configured in accordance with customer requirements.

A verifiable key structure linking the service provider key store 104, the host key store 108, and the VM key store 112 is generated as a result of the deployment and configuration of the host computer system 106 and the virtual computer system 110. The service provider deploys and allocates a number of host computer systems. The host computer systems are installed with host images and configured to act as host for virtual computing environments. Each host computer system includes a TPM. The service provider uses the TPM to confirm the proper configuration of each host computer system. In some implementations, the TPM generates a checksum of software and hardware configuration, and the checksum is confirmed against a database of approved checksums maintained by the service provider. In some implementations, the TPM ensures that only applications signed by an approved authority are executed on the host computer system 106. Each host computer system generates a Merkle tree of one-time-use cryptographic keys to be used by the host computer system. The root of the Merkle tree is published to the service provider. If the service provider determines that the host computer system 106 is properly configured, the root value of the Merkle tree associated with the host computer system 106 is gathered with other root values of Merkle trees associated with other computer systems to form a service provider Merkle tree. The service provider Merkle tree rolls up to a service provider hash. The service provider hash is published as a public key for the service provider.

When the host computer system 106 generates a new virtual computer system, the host computer system 106 causes a Merkle tree of one-time-use cryptographic keys to be generated for the virtual computer system. The root of the Merkle tree is signed using one of the one-time-use cryptographic keys generated above. In some implementations, the host computer system 106 performs various checks on the virtual computer system before signing the root of the Merkle tree of the virtual computer system 110. In some examples, the Merkle tree of one-time-use cryptographic keys is maintained by the virtual computer system 110 in the VM key store 112. In other implementations, the Merkle tree of one-time-use cryptographic keys is maintained in a TPM on the host computer system 106, and the virtual computer system 110 is granted access to the TPM to access the set of one-time-use cryptographic keys.

A client computer system 114 requests an attestation from the virtual computer system 110. The virtual computer system 110 performs the requested attestation, and signs the requested attestation with one of the one-time-use cryptographic keys provided to the virtual computer system 110. In some implementations, the virtual computer system 110 performs the requested attestation using a TPM on the host computer system 106, and the TPM signs the attestation with a one-time-use key assigned to the virtual computer system and retained by the TPM. The signed attestation is returned to the client computer system 114.

The signature on the attestation is verified by verifying that the signature on the attestation is properly generated with a one-time-use key from the Merkle tree associated with the virtual computer system 110. The root hash of the Merkle tree associated with the virtual computer system 110 is signed by the host computer system 106 using a one-time-use cryptographic key that links up to the root of a Merkle tree on the host key store 108. The root of the Merkle tree on the host key store 108 is a leaf node of the Merkle tree generated by the service provider and retained on the service provider key store 104. Therefore, the signature on the Merkle tree on the VM key store 112 can be verified up to the root node of the Merkle tree maintained on the service provider key store 104, which serves as the public key of the service provider. In various implementations, verification of the attestation may be used to indicate that the service provider computer system 102 has confirmed that the host computer system 106 is a properly configured host computer system operated by the service provider, that the host computer system 106 is hosting the virtual computer system 110, and that the virtual computer system 110 has confirmed a valid operating environment.

FIG. 2 shows an illustrative example of a computer system that manages host computer systems for a service provider. A block diagram 200 illustrates a structure of a service provider computer system 202 that provides host-management services for a service provider using a host management service 204. The host management service 204 includes a host manager 206, the key publication service 208, and host image manager 210. The host manager 206 is a service that tracks and manages a collection of host computer systems owned and operated by the service provider. The host manager 206 includes a database of host computer systems, and communicates management instructions to an agent on each host to perform configuration and other management tasks. The key publication service 208 is a network-accessible service that provides cryptographic hashes used for verifying digital signatures generated using cryptographic keys that are based at least in part on a public key of the service provider. The host image manager 210 works with the host manager 206 to provide imaging services to the host computer systems under the control of the service provider. The host management service 204 includes a host signature database 212. The host signature database 212 contains a database of environment signatures for the host computer systems that are under management. The service provider computer system 202 maintains a database of public keys 214 that are been assigned to host computer systems, a Merkle tree 216 of hashes cryptographically derived from the database of public keys 214, and a public key 218 at the root of the Merkle tree that acts as the public key of the service provider. Cryptographically derived from a value means using a one-way function at least once using inputs that are the values or derived from the values (possibly cryptographically derived from the values).

The host manager 206 contacts the hosts that are managed by the service provider, and verifies the configuration of each host using a TPM on each host. The configuration of the hosts may be verified by comparing a configuration signature provided by a TPM on each host against information in the host signature database 212. If a particular host is not configured, or is improperly configured, the host image manager 210 may be used to apply a clean image to the particular host. The host manager 206 retrieves a public key from each host that is determined to be properly configured, and the public keys are stored in the database of public keys 214. The host manager 206 generates the Merkle tree 216 from the public keys, resulting in the public key 218 of the service provider. The key publication service 208 publishes the public key 218 of the service provider, the Merkle tree 216, and the database of public keys 214. The key publication service 208 enables recipients of digital signatures to verify digital signatures against the public key 218 of the service provider.

FIG. 3 shows an illustrative example of a host computer system with a trusted platform module (“TPM”) that hosts one or more virtual computer system instances. A block diagram 300 shows a host computer system 302 that is operated by a service provider. The host computer system 302 may be a server computer, server cluster, computer appliance, or other computing device capable of hosting one or more virtual computing environments. The host computer system 302 includes a trusted platform module 304. In general, a trusted platform module is a hardware device comprising a secure cryptoprocessor and associated memory that provides support for encryption, decryption, a key generation, and other cryptographic operations in a protected tamper-resistant environment. The host computer system 302 also includes a virtual environment manager 305, and a virtualization runtime 306. The virtual environment manager 305 is a service running on the host computer system 302 that manages the creation, verification, and configuration of virtual computing environments on the host computer system 302. The virtual environment manager 305 interacts with a virtualization runtime 306. The virtualization runtime 306 is a runtime that supports virtual machines, container services, on-demand function execution, or other virtual computing environment. In the example shown in FIG. 3, the virtualization runtime 306 implements the first virtual computer system instance 308 and a second virtual computer system instance 310. The virtualization runtime 306 may support additional virtual computer systems, virtual machines, container runtimes, and other virtual computing environments.

The trusted platform module 304 includes an authentication service 312 and an authorization service 314. The authentication service 312 is a service within the trusted platform module that authenticates the identity of entities attempting to use the trusted platform module 304. The identity of entities attempting to use the trusted platform module 304 may be verified using digital certificates, passwords, or other credentials. The authorization service 314 determines whether a particular entity is authorized to perform a particular cryptographic operation. The authorization service 314 maintains a database of authorized entities and determines whether each request submitted to the trusted platform module 304 is allowable. The trusted platform module includes a cryptographic processor 316 and secure storage 318. In various implementations, the cryptographic processor may perform encryption, decryption, signing, key generation, random number generation, cryptographic hash determination, and other cryptographic operations. The secure storage 318 contains cryptographic keys, attestation keys, cryptographic hashes, Merkle trees, and other cryptographic information used by the trusted platform module 304.

The trusted platform module 304 contains a Merkle tree of one-time-use cryptographic keys that are linked into a corresponding Merkle tree maintained by the service provider. The Merkle tree within the trusted platform module 304 has a root node 320 that acts as a public key of the host computer system 302. The root node 320 is linked to a Merkle tree of hashes 322 that leads to a set of one-time-use cryptographic keys 324. The set of one-time-use cryptographic keys 324 is used by the virtual environment manager 305 to sign root nodes of hash trees that are associated with individual virtual computing environments. The first virtual computer system instance 308 includes a first hash tree of one-time-use cryptographic keys 326 and the second virtual computer system instance 310 includes a second hash tree of one-time-use cryptographic keys 328. The first hash tree of cryptographic keys 326 has a first root node that is signed using one of the one-time-use cryptographic keys 324 of the host computer system 302. The second hash tree of graphic keys 328 has a second root node that is signed using a different one-time-use cryptographic key of the one-time-use cryptographic keys 324.

Each time the virtual environment manager 305 generates a new virtual computing environment, the virtual environment manager 305 causes the new virtual computing environment to generate an associated hash tree of one-time-use cryptographic keys. The virtual environment manager 305 may use the trusted platform module 304 to verify the integrity of the new virtual computing environment. If the virtual environment manager 305 determines that the integrity of the new virtual computing environment is valid, the virtual environment manager 305 retrieves the root hash of the hash tree of one-time-use cryptographic keys of the new virtual computing environment, and signs the root hash with one of the host computer system's one-time-use cryptographic keys 324. The signed root hash is returned to the new virtual computing environment and may serve as proof that the new virtual computer system is running on a properly configured host computer system operated by the service provider.

FIG. 4 shows an illustrative example of a virtual computer system instance that is able to provide signed attestations of the computing environment. A block diagram 400 shows a virtual computer system instance 402 that is hosted by a host computer system operated by a service provider. The virtual computer system instance 402 includes a client operating system 404 that supports a client service 406. In other examples, the client operating system 404 supports a user program, a network service, or other client application deployed by a customer. The client operating system 404 includes a virtual client manager 408. The virtual client manager 408 receives an attestation request from the client service 406.

In response to the attestation request, the virtual client manager 408 performs operations to confirm the integrity of the virtual computer system instance. In some implementations, the virtual client manager uses the TPM installed on the host computer system that hosts the virtual computer system instance 402 to verify the configuration of the virtual computer system instance 402. If the virtual client manager 408 determines that the virtual computer system instance 402 is properly configured, the virtual client manager 408 signs an attestation to that effect using a digital signature generated with a one-time-use key selected from a set of one-time-use keys 414 issued to the virtual computer system instance 402 by the host of the virtual computer system instance 402. The set of one-time-use keys 414 is linked via a hash tree 412 to a root node of the hash tree 410. The root node of the hash tree 410 is signed using a one-time-use key owned by the host computer system of the virtual computer system instance 402. The signed attestation is returned to the client service 406.

The client service 406 retrieves the public key of the virtual computer system instance 402 from the client operating system 404 and verifies that the signature of the attestation is valid for the root node of the hash tree 410. To confirm the root node of the hash tree 410, the client service 406 retrieves verification hashes from a publication service operated by the service provider, and retrieves verification hashes from the host computer system. In some examples, verification hashes associated with the host computer system are retrieved from the TPM on the host computer system. The client service 406 verifies that the signature on the root node of the hash tree 410 can be verified using hash trees of the host computer system and the service provider to a root public key of the service provider. In this way, the client service 406 may verify that the integrity of the virtual computer system instance 402 has been verified by the virtual client manager 408, the host computer system of the virtual computer system instance 402, and the service provider.

FIG. 5 shows an illustrative example of a process that, as a result of being performed by a service provider, a host computer system, and a virtual computer system instance, generates and distributes a set of one-time-use cryptographic keys that are used by the virtual client computer system. A swim diagram 500 illustrates a process that begins at block 502 with a service provider computer system requesting an attestation from the host computer system. The service provider computer system may act as a signature authority for the service provider. In various examples, the attestation may be a request for a signature that represents the hardware and software configuration of the host computer system. In other examples, the attestation may be a request for configuration information relating to the host computer system. In yet another example, the attestation request may include instructions to be executed on a trusted platform module on the host computer system.

The host computer system receives the request from the service provider computer system, and the host computer system uses a trusted platform module on the host computer system to verify 504 the host configuration. In some examples, the TPM generates a signature representing the hardware and software configuration of the host computer system, and the TPM compares the signature against one or more approved signatures that correspond to verifiable hardware and software configurations. In some implementations, the authorized signatures are provided by the service provider computer system with the request. In other implementations, the authorized signatures are retained on the TPM on the host computer system.

If the host computer system is able to verify the hardware and software configuration of the host computer system, the host computer system generates 506 a set of one-time-use cryptographic keys for use by the host computer system. In some examples, the set of one-time-use cryptographic keys is comprised of Lamport or Winternitz keys. The host computer system generates a hash tree (also known as a Merkle tree) using hashes generated from the set of one-time-use cryptographic keys as leaf nodes, and linking to a root node hash that serves as a public key for the host computer system. At block 508, the host computer system uses the TPM to generate a signed attestation. In some examples, the signed attestation is a signature describing the hardware and software configuration of the host computer system that is signed using a private cryptographic key belonging to the TPM. At block 510, the host computer system provides the signed attestation and the root node hash to the service provider computer system.

The service provider computer system receives the signed attestation from the host computer system and verifies 512 both the signature on the attestation and the value of the attestation itself. In some examples, the service provider computer system uses a public key of the TPM to verify the signature on the attestation. The attestation itself is verified against a set of approved signatures maintained by the service provider computer system. The service provider computer system attempts to collect verifiable attestations from each of the host computer systems managed by the service provider. At block 514, the service provider computer system collects the root node hashes of the host computer systems that have also provided verified attestations to the service provider computer system. The root node hashes of the host computer systems are used by the service provider computer system to generate 514 a service-provider hash tree of the root node hashes. The service-provider hash tree has a root hash that is used as a public key for the service provider. At block 516, the service provider computer system publishes the root hash of the service-provider hash tree along with other hashes of the service-provider hash tree. Publication of the service-provider hash tree enables recipients of digital signatures generated with one-time-use keys controlled by host computer systems to verify the digital signatures against the public key of the service provider.

The host computer system uses the one-time-use keys generated at block 506 to provide additional one-time-use keys to virtual computer system instances managed by the host computer system. At block 518, the host computer system creates the virtual computer system instance and verifies the configuration of the virtual computer system instance. The host computer system verifies the integrity of the virtual computer system instance. In some examples, the host computer system uses the TPM to verify parts of the virtual runtime on the host computer system. In other examples, the host computer system uses the TPM to verify the image running on the virtual computer system instance. If the integrity of the virtual computer system instance cannot be verified, the virtual computer system instance is not provided with cryptographic keys that are signed by the host computer system. At block 520, if the integrity of the virtual computer system instance is verified, the host computer system generates a set of one-time-use cryptographic keys for use by the virtual computer system instance. Hashes of the set of one-time-use cryptographic keys are used to generate a hash tree that links the set of one-time-use cryptographic keys to a root hash which serves as a public key for the virtual computer system instance. At block 522, the host computer system signs the public key of the virtual computer system instance (root hash) using one of the one-time-use cryptographic keys generated by the host computer system at block 506.

The number of one-time-use cryptographic keys generated for use by the virtual computer system instance can be determined by the host computer system based on the projected needs of the individual virtual computer system instance. If additional keys are needed by the virtual computer system instance, the host computer system may generate an additional set of one-time-use cryptographic keys for the virtual computer system instance, generate an additional hash tree of the additional set of one-time-use cryptographic keys, and sign the new root of the additional hash tree.

The one-time-use cryptographic keys generated by the host computer system at block 520 are made available to the virtual computer system instance. In some examples, the one-time-use cryptographic keys and the associated hash tree are provided to the virtual computer system instance, and the virtual computer system instance receives and stores 526 the one-time-use cryptographic keys and the associated hash tree within the virtual computer system instance. In other examples, the one-time-use cryptographic keys are retained in a TPM on the host computer system, and TPM credentials are provided to the virtual computer system instance that allows the virtual computer system instance to access the one-time-use cryptographic keys on the TPM.

FIG. 6 shows an illustrative example of a process that, as a result of being performed by a client application and a virtual computer system instance, generates a signed attestation in response to a request from the client application. A swim diagram 600 illustrates a process that begins at block 602 with a client application requesting an attestation from the virtual computer system instance. The request may include a request for a signature representing the configuration of the virtual computer system instance, or the request may include a set of constraints to be evaluated and certified by the virtual computer system instance.

At block 604, the virtual computer system instance receives the request and acquires a configuration signature for the virtual computer system instance. In various examples, the configuration signature is a hash, checksum, or cyclic redundancy code (“CRC”) generated using measures of hardware and software configuration of the virtual computer system instance. In some examples, the virtual computer system instance generates the configuration signature based on the image running on the virtual computer system instance. In another example, the virtual computer system generates the signature based on cryptographic hashes of one or more software components running within the virtual computer system instance.

At block 606, the virtual computer system instance acquires a configuration signature for the host computer system hosting the virtual computer system instance. In some examples, the configuration signature of the host computer system is acquired by querying a service on the host computer system. In other examples, the configuration signature of the host computer system is acquired by generating a new host signature using a TPM on the host computer system. In yet another example, the virtual computer system instance queries the host computer system for the configuration signature, and the host computer system generates a new host signature if the configuration of the host computer system has changed. At block 608, the virtual computer system acquires a configuration signature for the service provider that operates the host computer system. In some examples, the configuration signature of the service provider is acquired by querying a service on a computer system operated by the service provider.

At block 610, the virtual computer system instance selects an unused key from the set of one-time-use cryptographic keys provided to the virtual computer system instance by the host computer system. The virtual computer system instance marks the selected key as used and generates 612 a digital signature for the configuration signatures using the selected one-time-use cryptographic key. At block 614, the virtual computer system instance sends the signed configuration signatures to the client application to be used as an attestation of system integrity.

The client application receives the signed attestation from the virtual computer system instance. At block 616, the client application verifies the signature on the attestation. In some examples, the signature on the attestation is verified by confirming the signature against the public key of the virtual computer system instance, and then verifying the signature on the public key of the virtual computer system instance against the public key of the service provider. At block 618, the client application examines the configuration signatures in the attestation and determines whether the configurations of the virtual computer system instance, the host computer system, and the service provider are acceptable. In some implementations, the client application retains a list of acceptable configuration signatures for the virtual computer system instance, the host computer system, and the service provider and compares the received configuration signatures against the list of acceptable configuration signatures. If the received configuration signatures are represented in the list of acceptable configuration signatures, the virtual computing environment of the virtual computer system instance is determined to be acceptable to the client application.

FIG. 7 shows an illustrative example of a process that, as a result of being performed by a recipient application, verifies a signed attestation provided by a virtual client computer system. A flowchart 700 illustrates a process that begins at block 702 with a recipient application receiving a signed attestation from a service on a virtual computer system. At block 704, the recipient application uses information within the attestation to confirm that the configuration of the virtual computer system matches a configuration that is acceptable to the recipient application. In some implementations, the recipient application compares the configuration signature of the attestation to a database of acceptable configuration signatures maintained by the application. If the configuration information in the attestation is acceptable to the recipient application, execution advances to block 706 and the recipient application verifies that the signature on the attestation is verifiable against a public key provided by the virtual computer system. In some implementations, the signature on the attestation is generated with a one-time-use cryptographic key, and the public key of the virtual computer system is a root of a hash tree built from hashes that includes a hash of the one-time-use cryptographic key.

The recipient application confirms that the public key provided by the virtual computer system is properly signed by the host computer system and the service provider. At block 708, the recipient application confirms that the signature on the public key of the virtual computer system is properly signed by the host computer system. The signature on the public key of the virtual computer system is signed using a one-time-use cryptographic key. The signature on the public key of the virtual computer system is verified using a hash tree and public key (root node of the hash tree) generated by and associated with the host computer system of the virtual computer system. The hash tree and public key of the host computer system are published by the host computer system. At block 710, the recipient application confirms that the public key of the host computer system is verifiable against the public key of the service provider. The service provider publishes a hash tree having a root node that represents the public key of the service provider. The public key of the host computer systems that are associated with the service provider are represented by the leaf nodes of the hash tree published by the service provider. The recipient application verifies that the public key of the host computer system is in the hash tree published by the service provider, and that the hash tree of the service provider properly chains up to the public key of the service provider.

After verifying the contents of the attestation and the signature on the attestation, at block 712, the recipient application determines that the configuration of the virtual computer system is acceptable. In some examples, the recipient application provides a challenge to the virtual computer system, and the virtual computer system signs the challenge with a digital signature. By verifying the digital signature against the public key of the host computer system and the service provider, the recipient application verifies that the service provider and the host computer system have attested to the proper configuration of the virtual computing environment.

FIG. 8 shows an illustrative example of a one-time-use cryptographic key that includes secret key pairs and corresponding public key pairs. A diagram 800 shows a one-time-use key that is generated by a signature authority. The one-time-use key is comprised of a secret key pair 802 and a public key pair 804. The secret key pair 802 includes a first secret key 806 and a second secret key 808. The first secret key 806 and the second secret key 808 each consist of a number (n) of n-bit keys. In some implementations, the first secret key 806 and the second secret key 808 are random numbers generated by the signature authority. In other implementations, the signature authority generates the first secret key 806 and the second secret key 808 from a secret seed value using a key derivation function (“KDF”). In some implementations, the secret seed value is itself generated from another secret seed value managed by the signature authority or owned by a superior signature authority.

The public key pair 804 includes a first public key 810 and a second public key 812. The first public key 810 and the second public key 812 each include a number (n) of n-bit hashes that correspond to the keys of the first secret key 806 and the second secret key 808. Each n-bit key of the secret key pair 802 is used to generate a corresponding n-bit hash of the public key pair 804. For example, the hash of the first key of the first secret key 806 is the first hash of the first public key 810. Each hash is generated with a cryptographic hash function or one-way function h(x)=y where y is easy to calculate for a given x, but x is computationally difficult to calculate for a given y. In some examples, SHA256, MD5, BLAKE, or BLAKE2 hash functions are used to generate the hashes. The public key pair 804 is published by the signature authority.

FIG. 9 shows an illustrative example of signing a message with a one-time-use cryptographic key. A diagram 900 illustrates the signing of a message 902 by a signature authority using a one-time-use key. In various examples, the message 902 may be a network packet, digital certificate, transactional record, media file, legal document, or other message submitted for signing by a requester. The signature authority receives the message 902 from the requester and determines an n-bit message hash 904 using a cryptographic hash function or other one-way function. A one-way function or cryptographic hash has the property that for a given input, a hash value is relatively easy to calculate, but for a given hash value, an input that produces the given hash value is comparatively difficult. In various examples, cryptographic hash functions such as SHA-256, MD-5, or BLAKE may be used as the cryptographic hash function.

To sign the message 902, the signature authority selects a one-time-use key for use in generating the digital signature. In some examples, if the signature authority has exhausted the supply of one-time-use keys, the signature authority reports an error and does not sign the message 902. In other examples, if the signature authority has used the supply of one-time-use keys, a key may be selected for reuse. A particular cryptographic key may be selected for reuse based at least in part on the number of times the particular key has been reused and the particular secret keys used to generate previous signatures. In some implementations, the signature authority maintains a key-use database that records the number of times each key has been used, and the digital signature generated with each key. In some examples, to locate a key for reuse, the signature authority may locate those keys that have been used the least number of times to generate digital signatures. In another example, the signature authority is provided with the message to be signed, and the signature authority identifies a cryptographic key for reuse that, when generating a digital signature for the message, reveals the lowest number of additional secret key portions of the available reusable cryptographic keys.

The one-time-use key includes a secret key pair that includes a first secret key 906 and a second secret key 908. For each bit (m) of the n-bit message hash 904, the signature authority selects either the m'th key from the first secret key if the bit is a zero bit, or the m'th key from the second secret key if the bit is a one bit. The selected keys are concatenated to form a digital signature 910 having n-squared bits. The digital signature 910 is provided to the requester. In addition to the digital signature 910, the requester is provided with public key information associated with the selected one-time-use key to support the verification of the digital signature 910. The public key information may include one or more hashes of a hash tree or Merkle tree that link the public key information to a public key of the signature authority. For each bit of the n-bit message hash 904, a secret key is chosen from either the first secret key 906 or the second secret key. For ‘zero’ bits of the n-bit message hash 904, a secret key corresponding to the bit in the n-bit message hash is selected from the first secret key 906. For ‘one’ bits of the n-bit message hash 904, a secret key corresponding to the bit in the n-bit message hash is selected from the second secret key 908. The bit position within the n-bit message hash 904 corresponds to the row (key number) within either the first secret key 906 or second secret key 908. In the example shown in FIG. 9, for each bit of the n-bit message hash, an arrow indicates the row of the particular secret key (having n-bits) which is added to the resulting digital signature 910.

FIG. 10 shows an illustrative example of verifying a message with a one-time-use cryptographic key. A diagram 1000 illustrates how a recipient of a signed message is able to verify a digital signature. To verify the signed message, the recipient separates a digital signature 1002 from the signed message. The digital signature 1002 has n-squared bits, and the recipient divides the digital signature 1002 into n-key portions of n-bits each. The recipient determines a hash of each key portion and assembles the hashes into a hash sequence 1004 of n, n-bit hashes.

Using information provided with the digital signature, the recipient identifies the particular one-time-use-key used to generate the digital signature and requests related public key information from a signature authority. The signature authority provides the recipient with a public key pair corresponding to the one-time-use key used to generate the digital signature. The public key pair includes a first set of public keys 1006 and a second set of public keys 1008.

The recipient extracts a message body 1010 from the signed message and uses a cryptographic hash function to determine an n-bit message hash 1012 for the message body 1010. For each bit (m) of the n-bit message hash 1012, the recipient determines whether the bit is a one or zero. If the bit is a zero, the recipient compares the m'th key of the first set of public keys 1006 to the m'th hash of the hash sequence 1004. If the bit is a one, the recipient compares the m'th key of the second set of public keys 1008 to the m'th hash of the hash sequence 1004. If any of the comparisons do not match, the signature is not valid for the provided message. If the comparisons match, the signature is valid. In some implementations, additional verifications are performed to confirm that the public keys provided are in compliance with a Merkle tree or hash tree maintained by a signature authority. For each bit of the n-bit message hash 1012, a public key is chosen from either the first set of public keys 1006 or the second set of public keys 1008. For ‘zero’ bits of the n-bit message hash 1012, a public key corresponding to the bit in the n-bit message hash is selected from the first set of public keys 1006. For ‘one’ bits of the n-bit message hash 1012, a public key corresponding to the bit in the n-bit message hash 1012 is selected from the second set of public keys 1008. The bit position within the n-bit message hash 1012 corresponds to the row (key number) within either the first set of public keys 1006 or second set of public keys 1008. In the example shown in FIG. 10, for each bit of the n-bit message hash, an arrow indicates the row of the particular public key (having n-bits) that is compared to the hash sequence 1004.

FIG. 11 shows an illustrative example of a secret key with an associated public key. A diagram 1100 shows a one-time-use cryptographic key 1102. The one-time-use cryptographic key 1102 comprises a secret key portion 1106 and a public key portion 1108 that is cryptographically derived from the secret key portion 1106 using a hash function 1110 such as a cryptographic hash or one-way function. In some examples, the public key portion is cryptographically derived from the secret key portion using a hash function such as a cryptographic hash or one-way function. In another example, the public key portion is cryptographically derived from the secret key portion using encryption. The one-time-use cryptographic key 1102 may be a key used in a Lamport signature scheme, a Winternitz signature scheme, or other one-time-use signature scheme using public and secret key pairs. In some implementations, the one-time-use cryptographic key 1102 is arranged in a hash tree, Merkle tree, or other structure where the public key portion 1108 is hashed with other public key portions of other one-time-use cryptographic keys into a single public key of a signature entity. In the following figures, the combination of the public key portion 1108 and the secret key portion 1106 may be represented as a public key/secret key pair.

FIG. 12 shows an illustrative example of a Merkle tree of one-time-use cryptographic keys. A diagram 1200 shows a binary Merkle tree that links a collection of one-time-use cryptographic keys 1202, 1204, 1206, 1208, 1210, 1212, 1214, and 1216 to a public key 1217 associated with a signature authority. Each one-time-use cryptographic key is comprised of a secret key and a public key cryptographically derived from the secret key using a cryptographic hash. In some examples, the secret key consists of n-pairs of n-bit secret keys, and the public key consists of n-pairs of n-bit hashes that correspond to the n-bit secret keys. The public keys are published by the signature authority, and the secret keys are maintained by the signature authority for use in generating digital signatures. A collection of corresponding level-0 hash nodes 1218, 1220, 1222, 1224, 1226, 1228, 1230, and 1232 is generated from the public keys of the one-time-use cryptographic keys. In some examples, each level-0 hash node is generated by taking a cryptographic hash of a public key of an associated one-time-use cryptographic key.

The level-0 hash nodes are incorporated into the Merkle tree. Pairs of level-0 hash nodes are combined using a cryptographic hash function to generate a set of four level-1 hash nodes 1234, 1236, 1238, and 1240. In the example shown in FIG. 12, hash 0,0 and hash 0,1 are concatenated and hashed to generate hash 1,0. Hash 0,2 and hash 0,3 are concatenated and hashed to generate hash 1,1. Hash 0,4 and hash 0,5 are concatenated and hashed to generate hash 1,2. Hash 0,6 and hash 0,7 are concatenated and hashed to generate hash 1,3. The four level-1 hash nodes are combined to generate two level-2 hash nodes 1242 and 1244. In the example shown in FIG. 12, hash 1,0 and hash 1,1 are concatenated and hashed to generate hash 2,0, and hash 1,2 and hash 1,3 are concatenated and hashed to generate hash 2,1. The level-2 hash nodes 1242 and 1244 are combined and hashed to produce the public key 1217. The public key 1217 is published by the signature authority so that recipients of a digital signature are able to confirm that the signature was generated with a one-time-use cryptographic key that is linked to the Merkle tree.

A recipient of a digital signature validates the signature using the public key information associated with the one-time-use cryptographic key used to generate the digital signature. The public key information is validated against the public key 1217 that is associated with a signature authority. The signature authority provides the recipient of the digital signature with the hash value nodes of the Merkle tree that are necessary to re-create the public key 1217 from the public key information.

For example, if the one-time-use cryptographic key 1206 is used to generate the digital signature, the public key information associated with the one-time-use cryptographic key 1206 is used to confirm that the digital signature was created from the secret key associated with the one-time-use cryptographic key 1206. The level-0 hash node 1222 can be re-created by the recipient using the public key information associated with the one-time-use cryptographic key 1206. In addition to the public key 1217, the signature authority provides the level-0 hash node 1224, the level-1 hash node 1234, and the level-2 hash node 1244. The recipient uses the determined level-0 hash node 1222 and the provided level-0 hash node 1224 to generate the level-1 hash node 1236. The recipient uses the generated level-1 hash node 1236 and the provided level-1 hash node 1234 to generate the level-2 hash node 1242. The generated level-2 hash node 1242 and the provided level-2 hash node 1244 are used to generate the public key 1217. If the generated public key matches the published public key provided by the signature authority, the one-time-use cryptographic key 1206 is a valid member of the Merkle tree. If the generated public key does not match the published public key, the one-time-use cryptographic key 1206 is not a valid member of the Merkle tree.

FIG. 13 shows an illustrative example of a number of linked Merkle trees that implement a cryptographic signature scheme for signing attestations. A diagram 1300 shows a cryptographic signature scheme for signing attestations. A set of one-time-use cryptographic keys 1302, 1304, 1306, and 1308 is provided to a host computer system. The set of one-time-use cryptographic keys is arranged in a Merkle tree. A first one-time-use cryptographic key 1302 and a second one-time-use cryptographic key 1304 are combined and hashed to generate a first intermediate hash 1310. A third one-time-use cryptographic key 1306 and the second one-time-use cryptographic key 1308 are combined and hashed to generate a second intermediate hash 1312. The first intermediate hash 1310 and the second intermediate hash 1312 are combined and hashed to generate a host root hash 1314.

The host root hash 1314 and other host root hashes generated by other host computer systems are provided to a service provider and integrated into a service-provider hash tree. Hashes of the host computer systems including the host root hash 1314 are combined and hashed to generate a first service-provider intermediate hash 1316 and a second service-provider intermediate hash 1318. The first service-provider intermediate hash 1316 and the second service-provider intermediate hash 1318 are combined and hashed to generate a service-provider root key 1320. The service-provider root key 1320 is published by the service provider, which enables entities that receive digital signatures generated using the set of one-time-use cryptographic keys 1302, 1304, 1306, and 1308 to verify that the digital signatures have been generated by host computer systems authorized by the service provider.

Host computer systems that generate virtual computing environments such as virtual machines use one of the set of one-time-use cryptographic keys 1302, 1304, 1306, and 1308 to sign a Merkle tree of one-time-use cryptographic keys provided to each virtual computing environment managed by the host computer system. In some examples, the host computer system generates a Merkle tree of one-time-use cryptographic keys for the virtual computing environment, and provides the Merkle tree of one-time use cryptographic keys to the virtual computing environment. In another example, the host computer system causes the TPM on the host computer system to generate the Merkle tree of one-time-use cryptographic keys, and provides the virtual computing environment with a credential that allows the virtual computing environment to access the Merkle tree of one-time-use cryptographic keys on the TPM. In yet another example, the virtual computing environment generates the Merkle tree of one-time-use cryptographic keys and provides the root node of the Merkle tree of one-time-use cryptographic keys to the host computer system.

The host computer system, after confirming the validity of the virtual computing environment, signs a root node of the Merkle tree 1322 with one of the set of one-time-use cryptographic keys 1302, 1304, 1306 or 1308. The root node of the Merkle tree 1322 is published by the virtual computing environment. The one-time-use keys 1324 and 1326 may be used by the virtual computing environment to generate signed attestations which may be provided to applications, end users, or other entities.

A recipient of a digital signature generated with one of the one-time-use keys 1324 or 1326 is able to verify the digital signature against the service-provider root key 1320. The recipient first confirms that the digital signature is generated with one of the one-time-use cryptographic keys issued to the virtual computing environment by regenerating the hashes from the particular key to the root node of the Merkle tree 1322. The root node of the Merkle tree 1322 is signed by a one-time-use key controlled by the host computer system hosting the virtual computing environment. The recipient confirms the hashes between the particular one-time-use cryptographic key of the host computer system to the host root hash 1314. The Merkle tree controlled by the service provider links to the host root hash, so the recipient is able to continue to confirm hashes up to the service-provider root key 1320.

FIG. 14 shows an illustrative example of an environment in which various embodiments may be practiced. A system diagram 1400 shows a signature authority 1402 that maintains a database of one-time-use keys 1404. The signature authority 1402 is a computer server, server cluster, virtual computer system, or other computing appliance configured with one or more services that generate and manage the one-time-use keys. Upon initialization, the signature authority 1402 generates a set of one-time-use keys. The set of one-time-use keys is of a finite fixed size. Each one-time-use key may be used to generate a digital signature. If a one-time-use key is used more than once, the cryptographic strength of the resulting digital signature is reduced with each additional use. Therefore, in some implementations, the signature authority 1402 maintains a record of key use to track or prevent the reuse of individual cryptographic keys.

The signature authority 1402 delegates signature authority to one or more authorized computer systems by providing a subset of the one-time-use keys to each authorized computer system. In the example shown in FIG. 14, the signature authority 1402 provides the first key set to a first authorized signing delegate 1406, a second key set to a second authorized signing delegate 1408, and a third key set to a third authorized signing delegate 1410. The signature authority 1402 provides the first authorized signing delegate 1406, the second authorized signing delegate 1408, and the third authorized signing delegate 1410 with non-overlapping subsets of the one-time-use keys. The signature authority 1402 maintains a record of the key subsets delegated. The signature authority 1402 may provide additional information such as key hashes, public keys, and revocation hashes to support the generation of digital signatures by the authorized signing delegates.

The number of cryptographic keys provided to each authorized signing delegate may be based on a predicted number of digital signatures to be generated by each of delegate. In some implementations, the signature authority 1402 predicts the number of digital signatures to be generated by each authorized delegate, and provides an appropriate number of cryptographic keys. In another implementation, each delegate requests a particular number of cryptographic keys based on a number of digital signatures predicted by the delegate. In some implementations, if a particular delegate runs out of cryptographic keys, the delegate may request and receive additional keys from the signature authority 1402. In another implementation, unused cryptographic keys may be returned from a delegate to the signature authority 1402.

In some implementations, the signature authority 1402 generates a set of secret revocation values and revocation hashes when the one-time-use keys are generated, and integrates the revocation hashes into a hash tree of the one-time-use keys. When a particular one-time-use key is revoked, the signature authority 1402 records the revocation in the database of one-time-use keys 1404, and publishes a secret revocation value associated with the revoked one-time-use key as proof of the signature authority's control over the one-time-use key.

FIG. 15 shows an illustrative example of a one-time-use cryptographic key that includes secret key pairs and corresponding public key pairs. A diagram 1500 shows a one-time-use key that is generated by a signature authority. The one-time-use key is comprised of a secret key pair 1502 and a public key pair 1504. The secret key pair 1502 includes a first secret key 1506 and a second secret key 1508. The first secret key 1506 and the second secret key 1508 each consist of a number (n) of n-bit keys. In some implementations, the first secret key 1506 and the second secret key 1508 are random numbers generated by the signature authority. In other implementations, the signature authority generates the first secret key 1506 and the second secret key 1508 from a secret seed value using a key derivation function (“KDF”). In some implementations, the secret seed value is itself generated from another secret seed value managed by the signature authority or owned by a superior signature authority.

The public key pair 1504 includes a first public key 1510 and a second public key 1512. The first public key 1510 and the second public key 1512 each include a number (n) of n-bit hashes that correspond to the keys of the first secret key 1506 and the second secret key 1508. Each n-bit key of the secret key pair 1502 is used to generate a corresponding n-bit hash of the public key pair 1504. For example, the hash of the first key of the first secret key 1506 is the first hash of the first public key 1510. Each hash is generated with a cryptographic hash function or one-way function h(x)=y where y is easy to calculate for a given x, but x is computationally difficult to calculate for a given y. In some examples, SHA256, MD5, BLAKE, or BLAKE2 hash functions are used to generate the hashes. The public key pair 1504 is published by the signature authority.

FIG. 16 shows an illustrative example of signing a message with a one-time-use cryptographic key. A diagram 1600 illustrates the signing of a message 1602 by a signature authority using a one-time-use key. In various examples, the message 1602 may be a network packet, digital certificate, transactional record, media file, legal document, or other message submitted for signing by a requester. The signature authority receives the message 1602 from the requester and determines an n-bit message hash 1604 using a cryptographic hash function or other one-way function. A one-way function or cryptographic hash has the property that for a given input, a hash value is relatively easy to calculate, but for a given hash value, an input that produces the given hash value is comparatively difficult. In various examples, cryptographic hash functions such as SHA-256, MD-5, or BLAKE may be used as the cryptographic hash function.

To sign the message 1602, the signature authority selects a one-time-use key for use in generating the digital signature. In some examples, if the signature authority has exhausted the supply of one-time-use keys, the signature authority reports an error and does not sign the message 1602. In other examples, if the signature authority has used the supply of one-time-use keys, a key may be selected for reuse. A particular cryptographic key may be selected for reuse based at least in part on the number of times the particular key has been reused and the particular secret keys used to generate previous signatures. In some implementations, the signature authority maintains a key-use database that records the number of times each key has been used, and the digital signature generated with each key. In some examples, to locate a key for reuse, the signature authority may locate those keys that have been used the least number of times to generate digital signatures. In another example, the signature authority is provided with the message to be signed, and the signature authority identifies a cryptographic key for reuse that, when generating a digital signature for the message, reveals the lowest number of additional secret key portions of the available reusable cryptographic keys.

The one-time-use key includes a secret key pair that includes a first secret key 1606 and a second secret key 1608. For each bit (m) of the n-bit message hash 1604, the signature authority selects either the m'th key from the first secret key if the bit is a zero bit, or the m'th key from the second secret key if the bit is a one bit. The selected keys are concatenated to form a digital signature 1610 having n-squared bits. The digital signature 1610 is provided to the requester. In addition to the digital signature 1610, the requester is provided with public key information associated with the selected one-time-use key to support the verification of the digital signature 1610. The public key information may include one or more hashes of a hash tree or Merkle tree that link the public key information to a public key of the signature authority. For each bit of the n-bit message hash 1604, a secret key is chosen from either the first secret key 1606 or the second secret key. For ‘zero’ bits of the n-bit message hash 1604, a secret key corresponding to the bit in the n-bit message hash is selected from the first secret key 1606. For ‘one’ bits of the n-bit message hash 1604, a secret key corresponding to the bit in the n-bit message hash is selected from the second secret key 1608. The bit position within the n-bit message hash 1604 corresponds to the row (key number) within either the first secret key 1606 or second secret key 1608. In the example shown in FIG. 16, for each bit of the n-bit message hash, an arrow indicates the row of the particular secret key (having n-bits) which is added to the resulting digital signature 1610.

FIG. 17 shows an illustrative example of verifying a message with a one-time-use cryptographic key. A diagram 1700 illustrates how a recipient of a signed message is able to verify a digital signature. To verify the signed message, the recipient separates a digital signature 1702 from the signed message. The digital signature 1702 has n-squared bits, and the recipient divides the digital signature 1702 into n-key portions of n-bits each. The recipient determines a hash of each key portion and assembles the hashes into a hash sequence 1704 of n, n-bit hashes.

Using information provided with the digital signature, the recipient identifies the particular one-time-use-key used to generate the digital signature and requests related public key information from a signature authority. The signature authority provides the recipient with a public key pair corresponding to the one-time-use key used to generate the digital signature. The public key pair includes a first set of public keys 1706 and a second set of public keys 1708.

The recipient extracts a message body 1710 from the signed message and uses a cryptographic hash function to determine an n-bit message hash 1712 for the message body 1710. For each bit (m) of the n-bit message hash 1712, the recipient determines whether the bit is a one or zero. If the bit is a zero, the recipient compares the m'th key of the first set of public keys 1706 to the m'th hash of the hash sequence 1704. If the bit is a one, the recipient compares the m'th key of the second set of public keys 1708 to the m'th hash of the hash sequence 1704. If any of the comparisons do not match, the signature is not valid for the provided message. If the comparisons match, the signature is valid. In some implementations, additional verifications are performed to confirm that the public keys provided are in compliance with a Merkle tree or hash tree maintained by a signature authority. For each bit of the n-bit message hash 1712, a public key is chosen from either the first set of public keys 1706 or the second set of public keys 1708. For ‘zero’ bits of the n-bit message hash 1712, a public key corresponding to the bit in the n-bit message hash is selected from the first set of public keys 1706. For ‘one’ bits of the n-bit message hash 1712, a public key corresponding to the bit in the n-bit message hash 1712 is selected from the second set of public keys 1708. The bit position within the n-bit message hash 1712 corresponds to the row (key number) within either the first set of public keys 1706 or second set of public keys 1708. In the example shown in FIG. 17, for each bit of the n-bit message hash, an arrow indicates the row of the particular public key (having n-bits) that is compared to the hash sequence 1704.

FIG. 18 shows an illustrative example of a secret key with an associated public key and a revocation key with an associated revocation hash value. A diagram 1800 shows a one-time-use cryptographic key 1802 and a one-time-use revocation value 1804. The one-time-use cryptographic key 1802 comprises a secret key portion 1806 and a public key portion 1808 that is cryptographically derived from the secret key portion 1806. Cryptographically derived from a value means using a one-way function at least once using inputs that are the values or derived from the values (possibly cryptographically derived from the values). In some examples, the public key portion 1808 is cryptographically derived from the secret key portion using a hash function 1810 such as a cryptographic hash or one-way function. In another example, the public key portion 1808 is cryptographically derived from the secret key portion using encryption. An encryption operation may be one-way to entities that do not have a corresponding decryption key. The one-time-use cryptographic key 1802 may be a key used in a Lamport signature scheme, a Winternitz signature scheme, or other one-time-use signature scheme using public and secret key pairs. In some implementations, the one-time-use cryptographic key 1802 is arranged in a hash tree, Merkle tree, or other structure where the public key portion 1808 is hashed with other public key portions of other one-time-use cryptographic keys into a single public key of a signature entity.

The one-time-use revocation value 1804 comprises a secret revocation value 1812 and a public revocation hash 1814 that is cryptographically derived from the secret revocation value 1812. In some examples, the public revocation hash 1814 is derived using a hash function 1816 such as a cryptographic hash or other one-way function. The hash function 1816 may be a cryptographic hash or other one-way function that is different from a hash function 1810 used to derive the public key portion 1808. In various implementations, the public revocation hash 1814 is combined with the public key portion 1808 to generate a hash value used to verify the integrity of a digital signature generated with the one-time-use cryptographic key 1802. A signature authority with control over the one-time-use cryptographic key 1802 may publish the secret revocation value 1812 as an indication that the one-time-use cryptographic key 1802 has been revoked and is no longer valid.

In the following figures, the combination of the public key portion 1808 and the secret key portion 1806 may be represented as a public key/secret key pair, and the combination of the public revocation hash 1814 and the secret revocation value 1812 may be represented as a revocation value/revocation hash pair.

FIG. 19 shows an illustrative example of a secret key with an associated revocation key that may be used to revoke the signature authority of the secret key. A diagram 1900 shows how a one-time-use cryptographic key 1902 and an associated revocation pair 1904 may be combined to create a revocable one-time-use cryptographic key. The one-time-use cryptographic key 1902 is comprised of a secret key and a public key cryptographically derived from the secret key. The revocation pair 1904 is comprised of a revocation value and a revocation hash cryptographically derived from the revocation value. In some examples, the revocation hash is based on a cryptographic hash or one-way function of the revocation value. The public key of the one-time-use cryptographic key 1902 and the revocation hash of the revocation pair 1904 are concatenated and fed to a hash function 1906. The hash function 1906 generates a linking hash 1908 for the combination of the one-time-use cryptographic key 1902 and the associated revocation pair 1904.

Each one-time-use cryptographic key is maintained by a signature authority in a structure as shown in FIG. 19, and each one-time-use cryptographic key has an associated revocation value. Authority over revoking a particular cryptographic key is controlled by the revocation value. In some examples, the signature authority retains control over the revocation values and determines whether a particular cryptographic key is revoked. In other examples, the signature authority delegates control over the revocation process by providing the revocation values to a delegated entity. In yet another example, the revocation values and revocation hashes are generated by a key-revocation authority, and the revocation hashes are provided to a signature authority. The signature authority incorporates the revocation hashes into the revocable key hash. The entity controlling the revocation values authorizes the revocation of one-time-use cryptographic keys by publishing the revocation values of the one-time-use cryptographic keys to be revoked.

A recipient that receives a cryptographic key or a message signed with the cryptographic key contacts the revocation authority to determine whether the cryptographic key has been revoked. The revocation authority maintains a database of revoked cryptographic keys and indicates to the recipient whether the cryptographic key is revoked. If the cryptographic key is revoked, the revocation authority provides a revocation value associated with the cryptographic key as proof that the cryptographic key was revoked by an authorized revocation authority. The recipient confirms the correctness of the revocation value by determining a hash of the revocation value, and combining the hash of the revocation value and a public key associated with the cryptographic key. If the hash of the combination matches the revocable key hash of the cryptographic key, the revocation value is valid. If the hash of the combinations does not match the revocable key hash of the cryptographic key, the revocation value is not valid and the key is not revoked.

FIG. 20 shows an illustrative example of a Merkle tree of one-time-use cryptographic keys. A diagram 2000 shows a binary Merkle tree that links a collection of one-time-use cryptographic keys 2002, 2004, 2006, 2008, 2010, 2012, 2014, and 2016 to a public key 2017 associated with a signature authority. Each one-time-use cryptographic key is comprised of a secret key and a public key derived from the secret key using a cryptographic hash. In some examples, the secret key consists of n-pairs of n-bit secret keys, and the public key consists of n-pairs of n-bit hashes that correspond to the n-bit secret keys. The public keys are published by the signature authority, and the secret keys are maintained by the signature authority for use in generating digital signatures. A collection of corresponding level-0 hash nodes 2018, 2020, 2022, 2024, 2026, 2028, 2030, and 2032 are generated from the public keys of the one-time-use cryptographic keys. In some examples, each level-0 hash node is generated by taking a cryptographic hash of a public key of an associated one-time-use cryptographic key.

The level-0 hash nodes are incorporated into the Merkle tree. Pairs of level-0 hash nodes are combined using a cryptographic hash function to generate a set of four level-1 hash nodes 2034, 2036, 2038, and 2040. In the example shown in FIG. 20, hash 0,0 and hash 0,1 are concatenated and hashed to generate hash 1,0. Hash 0,2 and hash 0,3 are concatenated and hashed to generate hash 1,1. Hash 0,4 and hash 0,5 are concatenated and hashed to generate hash 1,2. Hash 0,6 and hash 0,7 are concatenated and hashed to generate hash 1,3. The four level-1 hash nodes are combined to generate two level-2 hash nodes 2042 and 2044. In the example shown in FIG. 20, hash 1,0 and hash 1,1 are concatenated and hashed to generate hash 2,0, and hash 1,2 and hash 1,3 are concatenated and hashed to generate hash 2,1. The level-2 hash nodes 2042 and 2044 are combined and hashed to produce the public key 2017. The public key 2017 is published by the signature authority so that recipients of a digital signature are able to confirm that the signature was generated with a one-time-use cryptographic key that is linked to the Merkle tree.

A recipient of a digital signature validates the signature using the public key information associated with the one-time-use cryptographic key used to generate the digital signature. The public key information is validated against the public key 2017 that is associated with a signature authority. The signature authority provides the recipient of the digital signature with the hash value nodes of the Merkle tree that are necessary to re-create the public key 2017 from the public key information.

For example, if the one-time-use cryptographic key 2006 is used to generate the digital signature, the public key information associated with the one-time-use cryptographic key 2006 is used to confirm that the digital signature was created from the secret key associated with the one-time-use cryptographic key 2006. The level-0 hash node 2022 can be re-created by the recipient using the public key information associated with the one-time-use cryptographic key 2006. In addition to the public key 2017, the signature authority provides the level-0 hash node 2024, the level-1 hash node 2034, and the level-2 hash node 2044. The recipient uses the determined level-0 hash node 2022 and the provided level-0 hash node 2024 to generate the level-1 hash node 2036. The recipient uses the generated level-1 hash node 2036 and the provided level-1 hash node 2034 to generate the level-2 hash node 2042. The generated level-2 hash node 2042 and the provided level-2 hash node 2044 are used to generate the public key 2017. If the generated public key matches the published public key provided by the signature authority, the one-time-use cryptographic key 2006 is a valid member of the Merkle tree. If the generated public key does not match the published public key, the one-time-use cryptographic key 2006 is not a valid member of the Merkle tree.

FIG. 21 shows an illustrative example of a Merkle tree of one-time-use cryptographic keys that includes revocation keys for revoking portions of the tree. A diagram 2100 shows a Merkle tree of one-time-use cryptographic keys that includes revocation nodes for the internal nodes of the tree. The Merkle tree links a collection of one-time-use cryptographic keys 2102, 2104, 2106, 2108, 2110, 2112, 2114, and 2116 to a public key 2117 associated with a signature authority. Each one-time-use cryptographic key includes a secret key and a public key that is generated from the secret key using a cryptographic hash. Values associated with the various internal nodes of the Merkle tree are created by combining the values associated with the child nodes of the particular internal node, and determining a cryptographic hash of the combined value. In some implementations, the values associated with the child nodes are combined by concatenating the values associated with the various child nodes and determining a cryptographic hash of the concatenated value.

A set of eight level-0 hash nodes 2118, 2120, 2122, 2124, 2126, 2128, 2130, and 2132 is combined with four level-0 revocation pairs 2148, 2150, 2152, and 2154 to produce four level-1 hash nodes 2134, 2136, 2138, and 2140. Each revocation pair includes a revocation value and a revocation hash that is based on the revocation value. In the example shown in FIG. 21, the level-0 hash node 2118 and the level-0 hash node 2120 are combined with the revocation hash of revocation pair 2148 to produce the level-1 hash node 2134. The level-0 hash node 2122 and the level-0 hash node 2124 are combined with the revocation hash of revocation pair 2150 to produce the level-1 hash node 2136. The level-0 hash node 2126 and the level-0 hash node 2128 are combined with the revocation hash of revocation pair 2152 to produce the level-1 hash node 2138. The level-0 hash node 2130 and the level-0 hash node 2132 are combined with the revocation hash of revocation pair 2154 to produce the level-1 hash node 2140.

The set of four level-1 hash nodes 2134, 2136, 2138, and 2140 is combined with the revocation hashes of two level-1 revocation pairs 2156 and 2158 to produce two level-2 hash nodes 2142 and 2144. The level-1 hash node 2134 and the level-1 hash node 2136 are combined with the revocation hash of the level-1 revocation pair 2156 to produce the level-2 hash node 2142. The level-1 hash node 2138 and the level-1 hash node 2140 are combined with the revocation hash of the level-1 revocation pair 2158 to produce the level-2 hash node 2144. The two level-2 hash nodes 2142 and 2144 are combined with the level-2 revocation pair 2160 to produce the public key 2117.

The signature authority is able to use the revocation pairs to indicate revocation of a set of one-time-use cryptographic keys that are subordinate to a particular node of the Merkle tree by publishing the revocation value associated with the particular node. For example, by publishing the revocation value associated with the revocation pair 2150, the signature authority proves the revocation of the one-time-use cryptographic keys 2106 and 2108. In another example, the signature authority is able to revoke the one-time-use cryptographic keys 2110, 2112, 2114, and 2116 by publishing the revocation value associated with the revocation pair 2158.

In some implementations, each one-time-use cryptographic key shown in FIG. 21 is replaced with a structure that includes a corresponding revocation value as shown in FIG. 19, and the level-0 hashes are replaced with revocable one-time-use key hashes as shown in FIG. 19. In such implementations, the revocation authority may revoke an individual one-time-use cryptographic key by publishing the revocation value associated with the individual one-time-use cryptographic key.

In some implementations, the revocation pairs may be generated by a revocation authority other than the signature authority, and the revocation hashes are provided to the signature authority for inclusion in the Merkle tree. Particular one-time-use cryptographic keys are revoked by the revocation authority publishing one or more revocation values.

FIG. 22 shows an illustrative example of a set of seed values that are used to generate a set of one-time-use keys and corresponding public keys. A diagram 2200 illustrates a process whereby one or more seed values 2202 are used to generate a number of secret keys 2204. A corresponding collection of public keys 2206 is generated from the secret keys 2204 using a cryptographic hash function. In some examples, the one or more seed values 2202 is a single seed value that generates a plurality of secret keys. In another example, the one or more seed values 2202 is a plurality of seed values, each of which generates one or more secret keys. In yet another example, the one or more seed values 2202 is a plurality of related seed values, and each seed value generates a set of secret keys. For example, a master seed value may be used to generate a number of subordinate seed values, and each subordinate seed value is used to generate a subset of secret keys. An original seed value may be used to generate another seed value by applying a cryptographic hash or one-way function to the original seed value.

The secret keys 2204 are generated from the seed values 2202. Any number of secret keys may be generated from a single seed value. In some examples, the secret keys 2204 are generated using a key derivation function, key stretching algorithm, key strengthening algorithm, or cryptographic hash. In another example, the secret keys 2204 are generated using linear feedback shift register or pseudo-random number generation algorithm using the seed value as an initializer. The public keys 2206 are generated from the secret keys 2204 using a cryptographic hash or one-way function in accordance with the type of one-time-use cryptographic key desired by generating the one-time-use cryptographic keys from a set of seed values, and the seed values may be used as a shorthand to distribute subsets of the one-time-use cryptographic keys to delegate signature authorities.

FIG. 23 shows an illustrative example of a set of one-time-use cryptographic keys that are generated from a tree of seed values. A diagram 2300 illustrates a tree structure containing a collection of related seed values that are used to generate a collection of secret keys. The tree structure may be generated by a signature entity or other entity that is responsible for generating a collection of one-time-use cryptographic keys. A master seed 2302 controls the generation of the remaining seeds and the secret keys. The master seed 2302 is randomly generated by the signature entity. Each of the subordinate nodes of the master seed 2302 is generated by applying a one-way function or cryptographic hash to the value of the parent node, an optional salt value, and an index. For example, two child seed values are generated from the master seed 2302. Using a published cryptographic hash function, an optional salt value, and a node index, the signature authority generates a first level-2 seed 2304 (index-1) and a second level-2 seed 1006 (index=2). Each of the level-2 seed values is used to generate two additional subordinate seed values using the one-way function or cryptographic hash. The first level-2 seed 2304 is used to generate a first level-1 seed 2308 and a second level-1 seed 2310, and the second level-2 seed 2306 is used to generate a third level-1 seed 2312 and a fourth level-1 seed 2314.

The level-1 seed values are used to generate a collection of secret keys associated with one-time-use keys. The secret keys are derived from the level-1 seed values using a combination of a cryptographic hash and a key derivation function. The use of a cryptographic hash prevents the holder of a secret key from deriving the seed value used to generate the secret key and therefore prevents access to other secret keys derived from the same seed value. The key derivation function produces an output in a format that is appropriate for use as a secret key. In the example shown in FIG. 23, each level-1 seed value is used to generate two secret keys. The first level-1 seed 2308 is used to generate a first secret key 2316 and a second secret key 2318. The second level-1 seed 2310 is used to generate a first secret key 2320 and a second secret key 2322. The third level-1 seed 2312 is used to generate a first secret key 2324 and a second secret key 2326. The fourth level-1 seed 2314 is used to generate a first secret key 2328 and a second secret key 2330.

In many examples, the secret keys are used as the basis to create a collection of one-time-use cryptographic keys. The signature authority hashes the secret keys to produce a complementary set of public keys which are arranged in a Merkle tree. The Merkle tree may have a structure similar to the structure of the seeds used to produce the secret keys. Groups of one-time-use keys may be delegated to a subordinate signature authority by providing a seed value corresponding to a common parent node of the one-time-use keys to be delegated. Using the seed value, the subordinate signature authority may regenerate the secret keys for the corresponding nodes of the Merkle tree.

In other implementations, the structure of the tree used to organize the seed values is different from the structure of the Merkle tree. In some examples the tree of seed values may be constructed with a structure that matches an organizational structure, with the master seed being controlled by a central corporate authority, and internal nodes of the seed tree representing particular departments within the corporation. In other examples, the tree of seed values may be arranged in accordance with a hierarchy of potential signature delegates. In some implementations, the structure of the seed-value tree includes a root seed and an internal layer of seed nodes that can be delegated to one or more signature delegates. Each internal seed node is used to generate a number of secret keys that can be delegated as a unit. Regardless of the structure of the seed-value tree, the resulting secret keys are used to generate a corresponding set of public keys, and the public keys are hashed and linked to a Merkle tree.

FIG. 24 shows an illustrative example of a process that, as a result of being performed by a signature authority, generates a seed tree that supports delegation of one-time-use cryptographic keys. A flowchart 2400 illustrates a process that begins at block 2402 with the signature authority generating a master seed value. The master seed value is a random number and may be generated using hardware or software based on random number generation techniques. The master seed value is placed in a tree-node record allocated in memory by the signature authority. Each tree-node record includes one or more pointers that reference child nodes.

After generating the master seed value, the signature authority continues constructing the seed tree at block 2404. At block 2404, the signature authority initiates a loop that iterates over each level of the desired seed tree starting at the top with the master seed value node and ending one level above the leaf nodes. Within the above loop, at block 2406, the signature authority iterates over each tree-node at the iterated level. At block 2408, the signature authority generates child nodes for each iterated tree node. For each tree node, the signature authority allocates new child nodes in memory and sets pointers from the iterated tree node to each of the new child nodes. The signature authority generates a value for each new child node that is determined based on a function of the seed value of the iterated tree node and the position of the new child node. In some examples, the value of each new child node is determined by a function that takes the value of the seed of the parent node, the level of the parent node, the position of the parent node within the level, and the number of child nodes associated with the parent. The function by which the seed values of new child nodes are determined is a one-way function or cryptographic hash that prevents the derivation of parent seed values from child seed values.

At decision block 2410, the signature authority determines whether there are additional nodes at the currently iterated tree level. If there are additional nodes in the currently iterated tree level, execution returns to block 2406 and new child nodes for the next node in the iterated tree level are created. If there are not additional nodes in the currently iterated tree level, execution advances to decision block 2412. At decision block 2412, the signature authority determines whether there are additional levels of the seed tree to be processed. If there are additional levels of the seed tree to be processed, execution returns to block 2404 and the next level of the seed tree is processed. If there are not additional levels of the seed tree to be processed, execution advances to block 2414.

At block 2414, the signature authority generates secret keys from the lowest level of the seed tree. In some examples, the signature authority generates a single secret key from each seed node at the bottom of the seed tree. In another example, the signature authority generates a number of secret keys from each seed node at the bottom of the seed tree. In some examples, the secret keys are generated using a combination of a one-way function or cryptographic hash and a key derivation function so that the secret keys may not be used to easily derive the seed value. In another example, the secret keys are generated using a key derivation function that uses the seed value as input.

FIG. 25 shows an illustrative example of a process that, as a result of being performed by a signature authority, delegates a portion of one-time-use cryptographic keys to an authorized entity. A flowchart 2500 illustrates a process that begins at block 2502 with a signature authority receiving a request from a prospective delegate to generate digital signatures on behalf of the signature authority. To generate the digital signatures, the prospective delegate requests a number of one-time-use keys from the signature authority. The perspective delegate may be a server, server cluster, or other computing entity operated by a business, department, or subsidiary of the signature authority. The signature authority authenticates the identity of the prospective delegate using a combination of digital certificates, biometric measures, or multiply-factor authentication techniques. After authenticating the prospective delegate, the signature authority may consult an authorization database to confirm that the prospective delegate is authorized to generate signatures on behalf of the signature authority. If the prospective delegate is authorized to generate signatures on behalf of the signature authority, execution advances to decision block 2504.

At decision block 2504, the signature authority examines a store of one-time-use keys that are maintained by the signature authority for generating digital signatures. The store includes information that describes which of the one-time-use keys have been previously used to generate digital signatures. If the number of one-time-use keys requested by the prospective delegate is greater than the number of one-time-use keys that have not yet been used to generate a digital signature, execution advances to block 2506 and the signature authority generates an error. At block 2506, the signature authority indicates to the prospective delegate that there are insufficient one-time-use keys available to satisfy the request, and the request is denied.

If there are sufficient one-time-use keys available to satisfy the request, execution advances to block 2508. At block 2508, the signature authority identifies one or more seed values that can be used to delegate an appropriate set of secret keys to the prospective delegate. The one or more seed values are selected so that the children of the one or more seed values represent the number of secret keys requested. For example, if the prospective delegate requests four one-time-use keys, the signature authority will identify a seed value that can be used to generate four previously unused one-time-use keys. For example, in FIG. 23, the seed 2306 may be provided since it may be used to generate the four secret keys 2324, 2326, 2328, and 2330. In some examples, a number of seed values may be provided. If the prospective delegate requests six secret keys, the signature authority may provide a first seed value that can be used to generate two previously unused one-time-use keys, and a second seed value that can be used to generate four previously unused one-time-use keys.

At block 2510, the signature authority identifies a set of intermediate hashes that will allow the prospective delegate to verify signatures generated with the identified seed values. In some implementations, the structure of the seed tree matches the structure of a Merkle tree that is associated with the one-time-use keys. The signature authority identifies the interior nodes of the Merkle tree that correspond to the seed values to be delegated to the prospective delegate. For each identified interior node of the Merkle tree, the signature authority identifies hash nodes between the identified interior node and the root of the Merkle tree that are used to verify digital signatures subordinate to the identified interior node. If more than one seed value is delegated to the prospective delegate, a corresponding number of hash-node sets are identified to allow the prospective delegate to verify digital signatures.

At block 2512, the signature authority provides the seed values to be delegated, the positions of the seed values within the Merkle tree, and the hash-node sets to the prospective delegate. The delegate uses the seed values to generate a set of secret keys and corresponding public key pairs that are usable as one-time-use keys. The one-time-use keys may be used to generate digital signatures, and the digital signatures may be verified using the Merkle tree by confirming the hashes of the public key pairs against the root of the Merkle tree which is owned by the signature authority.

FIG. 26 shows an illustrative example of a process that, as a result of being performed by an authorized signature delegate, signs a message using a one-time-use cryptographic key provided by a signature authority. A flowchart 2600 illustrates a process that begins at block 2602 with a delegate receiving a request to sign a message from a requester. The delegate has a set of seed values and supporting information that are usable to generate a set of one-time-use cryptographic keys that are verifiable against the public key owned by the signature authority. The delegate authenticates the requester and confirms that the request is authorized. If the signature request is authorized, execution advances to decision block 2604.

At decision block 2604, the delegate determines whether the delegate has an unused one-time-use cryptographic key with which to generate a digital signature. If the delegate does not have an unused one-time-use cryptographic key, execution advances to block 2606. At block 2606, the delegate generates an error and indicates to the requester that insufficient signing keys are available. In some implementations, the delegate requests additional one-time-use cryptographic keys from the signature authority. In yet another implementation, the delegate identifies a one-time-use cryptographic key from the set of one-time-use cryptographic keys previously allocated to the delegate for reuse. In some implementations, the delegate maintains a first counter of keys allocated by the signature authority, and a second counter of keys used to generate digital signatures in order to identify when unused keys are available. If at least one one-time-use cryptographic key is available, execution advances to block 2608.

At block 2608, the delegate uses the seed values allocated to the delegate by the signature authority to generate a set of secret keys. In some implementations, the delegate generates a complete set of secret keys from the seed values allocated to the delegate and stores the set of secret keys in a data store to be used as needed. The delegate tracks which secret keys have been previously used to generate digital signatures, and selects a particular set of secret keys that have not yet been used to generate the requested digital signature. After selecting the particular set of secret keys, the signature authority determines 2610 a hash value for the message to be signed, and uses the hash value and the generated set of secret keys to generate a signature for the message. In some examples, the signature is generated in accordance with the process shown and described in FIG. 16. After generating the signature, delegate records that the one-time-used key associated with the particular set of secret keys has been used.

At block 2612, the delegate uses the set of secret keys to generate a corresponding set of public keys to be used in verifying the signature. The public keys may be generated by determining a cryptographic hash of each secret key in the set of secret keys as described in FIG. 15. At block 2614, the delegate uses the public keys to generate a set of cryptographic hashes that are arranged in a Merkle tree. The Merkle tree generated by the delegate connects to a parent Merkle tree maintained by the signature authority. At block 2616, the delegate retrieves hash information from the parent Merkle tree from the signature authority that allows the delegate to verify digital signatures generated by the delegate against a root public key owned by the signature authority. In some examples, the signature authority provides the hash values associated with the child nodes of each node in the Merkle tree from the root node to the interior node associated with the each seed value delegated to the delegate.

At block 2618, the delegate assembles the signature and the supporting information to be provided to the requester. The delegate assembles and provides the signature of the message, information that identifies the one-time-use key used to sign the message, the public key of the one-time-use key used to sign the message, and the intermediate hashes necessary to verify the signature against the root hash of the Merkle tree maintained by the signature authority. Using the provided information, the recipient is able to verify that the signature of the message matches the public keys of the one-time-use key, and that the public keys of the one-time-use key are linked to the Merkle tree and to the root of the Merkle tree which is maintained by the signature authority. Therefore, although the signature is generated and provided by the delegate, it can be validated against the signature authority's public key, even though the delegate may not have access to all of the one-time-use keys controlled by the signature authority.

FIG. 27 shows an illustrative example of a delegation service that allocates and distributes blocks of cryptographic keys to one or more authorized delegates. A system diagram 2700 shows a key delegation server 2702 operated by a signature authority that provides blocks of one-time-use cryptographic keys to a delegate computer system 2704. The key delegation server 2702 is a computer system, computer server or server cluster that includes a processor and memory. The memory contains instructions that implement one or more services. The key delegation server 2702 maintains a Merkle tree of delegable keys 2706 in a memory on the key delegation server 2702. The delegable keys 2706 are one-time-use cryptographic keys such as Lamport keys or Winternitz keys that are used to generate digital signatures. The key delegation server 2702 includes a key delegation interface 2708, a key publication service 2710, and a key delegation service 2712.

The key delegation interface 2708 is a public interface that allows potential signature delegates to request blocks of one-time-use cryptographic keys from the key delegation server 2702. The key delegation interface 2708 accesses a delegate database 2714 that contains information identifying authorized delegates, and the particular one-time-use cryptographic keys allocated to particular authorized delegates. The key delegation interface 2708 includes an authentication service 2716 and an authorization service 2718. When a delegate contacts the key delegation server 2702, the authentication service 2716 within the key delegation interface 2708 confirms the identity of the delegate using a digital certificate, user-password combination, fingerprint or other biometric. After the delegate has been authenticated, the authorization service 2718 queries the delegate database 2714 and determines whether the delegate is authorized to generate signatures on behalf of the signature authority. The information in the delegate database 2714 may be maintained by an administrator of the signature authority, and may include restrictions on the number of one-time-use keys that may be assigned to a particular delegate.

The key publication service 2710 includes a key revocation service 2720 and a verification service 2722. The key publication service 2710 is used by entities that generate and verify digital signatures. The key publication service 2710 accesses the Merkle tree of delegable keys 2706 and makes available public keys and hashes that allow a particular digital signature generated with a one-time-use key to be verified. For example, when an entity contacts the key publication service 2710 to verify a digital signature, the verification service 2722 within the key publication service 2710 queries the Merkle tree of delegable keys 2706 to acquire the hashes within the Merkle tree that are necessary to confirm the link between the digital signature and the public key of the signature entity.

In some implementations, the key publication service 2710 includes a key revocation service 2720. The key revocation service provides information regarding the revocation of one-time-use cryptographic keys. When verifying a digital signature, the verifying entity contacts the key revocation service 2720 and queries whether the cryptographic key used to generate the digital signature is still valid. The key revocation service 2720 queries the Merkle tree of delegable keys 2706, and if the cryptographic key is marked as invalid, the key revocation service 2720 provides the verifying entity with a revocation value associated with the revoked cryptographic key. The verifying entity confirms the validity of the revocation value by hashing the revocation value and combining the revocation hash with intermediate hashes in the Merkle tree to reproduce the public key of the signature authority. In some examples, the key revocation service 2720 maintains a revocation database that indicates which keys have been revoked. The revocation database may be a relational database, hash table, list. In some implementations, the revocation database is implemented using a blockchain.

The delegate computer system 2704 may contact the key delegation server 2702 to acquire additional blocks of one-time-use cryptographic keys as needed to generate digital signatures. When the delegate computer system 2704 sends a request for keys to the key delegation server 2702, the request is received by the key delegation interface 2708. The key delegation interface authenticates the delegate computer system 2704 and authorizes the request. The request is forwarded to the key delegation service 2712, and the key delegation service 2712 identifies a set of one-time-use cryptographic keys from the Merkle tree of delegable keys 2706. The set of one-time-use cryptographic keys is marked as being allocated to the delegate computer system 2704, and the delegate database 2714 is updated to record the keys that are allocated to the delegate computer system 2704. The key delegation service 2712 returns the requested one-time-use cryptographic keys to the delegate computer system 2704. The key delegation service 2712 provides information to the key publication service 2710 indicating the additional one-time-use cryptographic keys that are been allocated to the delegate computer system 2704. Using information from the delegate database 2714, the verification service 2722 identifies the intermediate hashes necessary to verify digital signatures generated using the additional one-time-use cryptographic keys, and provides the intermediate hashes to the delegate computer system 2704. In some implementations, the key publication service 2710 identifies verification information that has already been provided to the delegate computer system, and provides only the additional verification information not already in the possession of the delegate computer system 2704.

FIG. 28 shows an illustrative example of a process that, as a result of being performed by a key distribution service and a delegate, allocates a block of keys managed by the distribution service to be used by the delegate. A swim diagram 2800 illustrates a process that begins at block 2802 with the delegate estimating a number of digital signatures to be generated on behalf of the signature authority. The number of digital signatures may be estimated based on previous signature generation over a period of time or based on a number of pending messages to be signed. At block 2804, the delegate sends a request specifying the number of one-time-use keys desired to the distribution service.

At block 2806, the distribution service receives the request from the delegate and authenticates the delegate using a digital certificate, a username/password, or other authentication credential. At block 2808, the distribution service determines whether the delegate is authorized to generate digital signatures on behalf of the signature authority by consulting a database of authorized delegate information. If the delegate is authorized to generate digital signatures on behalf of the signature authority, execution advances to block 2810 and the distribution service consults a database of one-time-use cryptographic keys to determine whether there are sufficient unused one-time-use cryptographic keys to satisfy the request. If there are not sufficient unused one-time-use cryptographic keys to satisfy the request, the distribution service responds with an error message to the delegate. Otherwise, the distribution service selects 2812 a set of one-time-use cryptographic keys to be provided to the delegate. The selected set of keys may be chosen from a Merkle tree such that the set of keys descends from a common internal node of the Merkle tree. If there is not a common internal node of the Merkle tree, the selected set of keys may be chosen so that the set of keys comprises a minimum number of internal nodes of the Merkle tree. The selected keys may be provided to the delegate by providing the secret and private key pairs themselves, or by providing seed values associated with the internal nodes of the Merkle tree that are parents of the set of keys as described elsewhere in this document.

At block 2814, the distribution service records that the selected keys have been delegated to the delegate. Delegation of the selected keys may be recorded as a property within the nodes of the Merkle tree or within a database of delegate information maintained by the signature authority. At block 2816, the distribution service identifies supporting information necessary for key verification. The supporting information includes public keys and hash values from the Merkle tree that are used to verify digital signatures created with the set of delegated keys. At block 2818, the distribution service assembles the set of keys and the supporting information, and provides the set of keys and the supporting information to the delegate. In some implementations, the set of keys are provided by providing the secret and public portions of the keys themselves. In other implementations, the set of keys are provided by providing seed values that may be used to generate the secret portions of the keys to be delegated.

At block 2820, the delegate receives the keys and the supporting information from the key distribution service. Using the keys and supporting information, the delegate is able to sign messages with digital signatures, and the digital signatures produced are able to be verified against a public key maintained by the signature authority.

FIG. 29 shows an illustrative example of a process that, as a result of being performed by a signature authority and a key generator, generates a subset of one-time-use keys specified by the signature authority using an intermediate seed value. A swim diagram 2900 illustrates a process that begins at block 2902 with a signature authority generating a random seed value to be used in generating a set of one-time-use cryptographic keys. The random seed value may be generated using a hardware random number generator or with pseudorandom number generation techniques. After generating the random root seed value, the signature authority determines 2904 the parameters of a seed tree. The seed tree contains a set of intermediate seed values that are derived from the root seed value. In some examples, the intermediate seed values are derived from the root seed value using a cryptographic hash or other one-way function. The generation of the intermediate seed values is governed by a tree-depth parameter and a fanout parameter. The tree-depth parameter and the fanout parameter are based at least in part on the desired number of one-time-use cryptographic keys to be generated. In one example, the fanout parameter is to and the seed tree is a binary tree, and the depth of the seed tree is selected to provide a number of one-time-use cryptographic keys greater than or equal to the desired number of one-time-use script a graphic keys.

After determining the parameters of the seed tree, the signature authority generates 2906 the intermediate seed values. In some implementations, the intermediate seed values are determined by calculating a cryptographic hash of the value of the parent node plus the position of the child node being generated. For example, the first child node of a particular seed node is determined by calculating the cryptographic hash of the value of the parent node plus one, and the second child node of the particular seed node is determined by calculating the cryptographic hash of the value of the parent node plus two. The signature authority distributes 2908 the intermediate seed values to one or more authorized key generators. The key generators are a service running on a computer system that works in coordination with the signature authority to distribute the generation of one-time-use cryptographic keys. In some examples, the key generators are also able to perform digital signatures on behalf of the signature authority. In other examples, the key generators assist the signature authority by generating a portion of the one-time-use cryptographic keys, and supply a root hash for the portion of one-time-use cryptographic keys that each generator produces. In yet another example, the key generators provide the signature authority with the one-time-use cryptographic keys that are generated in addition to the hash values associated with the generated one-time-use cryptographic keys.

At block 2910, the key generator receives the intermediate seed value from the signature authority. In some examples, the signature authority provides the key generator with parameters of the subset of the seed tree represented by the intermediate seed value. The parameters may include a fanout and depth of the subset of the seed tree to be generated by the key generator. In yet another example, the signature authority specifies a seed generation algorithm and/or a key-generation algorithm to be used in generating the subset of the seed tree. The key generator generates subordinate seed values from the intermediate seed value in accordance with any parameters provided by the signature authority.

At block 2912, the key generator generates secret portions of one-time-use keys from leaf nodes of the subset of the seed tree generated by the key generator. In some examples, the secret portions of the one-time-use keys are generated using a cryptographic hash or one-way function and a key derivation function. The cryptographic hash or one-way function prevents a recipient of the one-time-use key from deriving the seed value used to generate the key, and the key derivation function transforms the resulting pseudorandom number into a format suitable for use as a key. In some examples, the secret portions of the one-time-use keys are a collection of key pairs. At block 2914, the key generator generates public portions of the one-time-use keys from the secret portions of the one-time-use keys. In some examples, the public portions of the one-time-use keys are generated by applying a cryptographic hash to the secret portions of the one-time-use keys. In one implementation, the secret portions of the one-time-use keys are pseudorandom key pairs, and the public portions of the one-time-use keys are corresponding pairs of hashes of each pseudorandom key pair.

At block 2916, the key generator generates a subordinate Merkle tree of the public portions of the one-time-use keys. The public portions of the one-time-use keys are hashed to produce a set of corresponding hashes. The corresponding hashes are used as the leaf nodes of the Merkle tree, and the key generator completes the Merkle tree using a tree geometry that corresponds to the geometry of the subset of the seed tree generated earlier. After generating the Merkle tree, the key generator provides 2918 the root hash of the Merkle tree to the signature authority. In some implementations, the key generator provides the entire Merkle tree. In yet another implementation, the key generator provides the one-time-use keys generated by the key generator in addition to the Merkle tree.

At block 2920, the signature authority receives the hashes from the key generator. The signature authority uses the root hash provided by the key generator to complete a master hash tree of one-time-use keys that are managed by the signature authority. The master hash tree may include additional root hashes generated by other subordinate signature authorities. In some examples, the signature authority combines the hashes provided by the key generator with hashes provided by other key generators to complete a master hash tree for the entire set of one-time-use keys. In this way, the signature authority may distribute the task of generating one-time-use keys amongst a set of trusted key-generating entities resulting in faster key generation.

FIG. 30 illustrates aspects of an example environment 3000 for implementing aspects in accordance with various embodiments. As will be appreciated, although a web-based environment is used for purposes of explanation, different environments may be used, as appropriate, to implement various embodiments. The environment includes an electronic client device 3002, which can include any appropriate device operable to send and/or receive requests, messages, or information over an appropriate network 3004 and, in some embodiments, convey information back to a user of the device. Examples of such client devices include personal computers, cell phones, handheld messaging devices, laptop computers, tablet computers, set-top boxes, personal data assistants, embedded computer systems, electronic book readers, and the like. The network can include any appropriate network, including an intranet, the Internet, a cellular network, a local area network, a satellite network, or any other such network and/or combination thereof. Components used for such a system can depend at least in part upon the type of network and/or environment selected. Many protocols and components for communicating via such a network are well known and will not be discussed herein in detail. Communication over the network can be enabled by wired or wireless connections and combinations thereof. In this example, the network includes the Internet and/or other publicly addressable communications network, as the environment includes a web server 3006 for receiving requests and serving content in response thereto, although for other networks an alternative device serving a similar purpose could be used as would be apparent to one of ordinary skill in the art.

The illustrative environment includes at least one application server 3008 and a data store 3010. It should be understood that there can be several application servers, layers, or other elements, processes, or components, which may be chained or otherwise configured, which can interact to perform tasks such as obtaining data from an appropriate data store. Servers, as used herein, may be implemented in various ways, such as hardware devices or virtual computer systems. In some contexts, servers may refer to a programming module being executed on a computer system. As used herein, unless otherwise stated or clear from context, the term “data store” refers to any device or combination of devices capable of storing, accessing and retrieving data, which may include any combination and number of data servers, databases, data storage devices, and data storage media, in any standard, distributed, virtual, or clustered environment. The application server can include any appropriate hardware, software, and firmware for integrating with the data store as needed to execute aspects of one or more applications for the client device, handling some or all of the data access and business logic for an application. The application server may provide access control services in cooperation with the data store and is able to generate content including, but not limited to, text, graphics, audio, video, and/or other content usable to be provided to the user, which may be served to the user by the web server in the form of HyperText Markup Language (“HTML”), Extensible Markup Language (“XML”), JavaScript, Cascading Style Sheets (“CSS”), JavaScript Object Notation (JSON), and/or another appropriate client-side structured language. Content transferred to a client device may be processed by the client device to provide the content in one or more forms including, but not limited to, forms that are perceptible to the user audibly, visually, and/or through other senses. The handling of all requests and responses, as well as the delivery of content between the client device 3002 and the application server 3008, can be handled by the web server using PHP: Hypertext Preprocessor (“PHP”), Python, Ruby, Perl, Java, HTML, XML, JSON, and/or another appropriate server-side structured language in this example. Further, operations described herein as being performed by a single device may, unless otherwise clear from context, be performed collectively by multiple devices, which may form a distributed and/or virtual system.

The data store 3010 can include several separate data tables, databases, data documents, dynamic data storage schemes and/or other data storage mechanisms and media for storing data relating to a particular aspect of the present disclosure. For example, the data store illustrated may include mechanisms for storing production data 3012 and user information 3016, which can be used to serve content for the production side. The data store also is shown to include a mechanism for storing log data 3014, which can be used for reporting, analysis, or other such purposes. It should be understood that there can be many other aspects that may need to be stored in the data store, such as page image information and access rights information, which can be stored in any of the above listed mechanisms as appropriate or in additional mechanisms in the data store 3010. The data store 3010 is operable, through logic associated therewith, to receive instructions from the application server 3008 and obtain, update, or otherwise process data in response thereto. The application server 3008 may provide static, dynamic, or a combination of static and dynamic data in response to the received instructions. Dynamic data, such as data used in web logs (blogs), shopping applications, news services, and other such applications may be generated by server-side structured languages as described herein or may be provided by a content management system (“CMS”) operating on, or under the control of, the application server. In one example, a user, through a device operated by the user, might submit a search request for a certain type of item. In this case, the data store might access the user information to verify the identity of the user and can access the catalog detail information to obtain information about items of that type. The information then can be returned to the user, such as in a results listing on a web page that the user is able to view via a browser on the client device 3002. Information for a particular item of interest can be viewed in a dedicated page or window of the browser. It should be noted, however, that embodiments of the present disclosure are not necessarily limited to the context of web pages, but may be more generally applicable to processing requests in general, where the requests are not necessarily requests for content.

Each server typically will include an operating system that provides executable program instructions for the general administration and operation of that server and typically will include a computer-readable storage medium (e.g., a hard disk, random access memory, read only memory, etc.) storing instructions that, when executed (i.e., as a result of being executed) by a processor of the server, allow the server to perform its intended functions.

The environment, in one embodiment, is a distributed and/or virtual computing environment utilizing several computer systems and components that are interconnected via communication links, using one or more computer networks or direct connections. However, it will be appreciated by those of ordinary skill in the art that such a system could operate equally well in a system having fewer or a greater number of components than are illustrated in FIG. 30. Thus, the depiction of the system 3000 in FIG. 30 should be taken as being illustrative in nature and not limiting to the scope of the disclosure.

The various embodiments further can be implemented in a wide variety of operating environments, which in some cases can include one or more user computers, computing devices, or processing devices which can be used to operate any of a number of applications. User or client devices can include any of a number of computers, such as desktop, laptop, or tablet computers running a standard operating system, as well as cellular, wireless, and handheld devices running mobile software and capable of supporting a number of networking and messaging protocols. Such a system also can include a number of workstations running any of a variety of commercially available operating systems and other known applications for purposes such as development and database management. These devices also can include other electronic devices, such as dummy terminals, thin-clients, gaming systems, and other devices capable of communicating via a network. These devices also can include virtual devices such as virtual machines, hypervisors, and other virtual devices capable of communicating via a network.

Various embodiments of the present disclosure utilize at least one network that would be familiar to those skilled in the art for supporting communications using any of a variety of commercially available protocols, such as Transmission Control Protocol/Internet Protocol (“TCP/IP”), User Datagram Protocol (“UDP”), protocols operating in various layers of the Open System Interconnection (“OSI”) model, File Transfer Protocol (“FTP”), Universal Plug and Play (“UpnP”), Network File System (“NFS”), Common Internet File System (“CIFS”), and AppleTalk. The network can be, for example, a local area network, a wide-area network, a virtual private network, the Internet, an intranet, an extranet, a public switched telephone network, an infrared network, a wireless network, a satellite network, and any combination thereof. In some embodiments, connection-oriented protocols may be used to communicate between network endpoints. Connection-oriented protocols (sometimes called connection-based protocols) are capable of transmitting data in an ordered stream. Connection-oriented protocols can be reliable or unreliable. For example, the TCP protocol is a reliable connection-oriented protocol. Asynchronous Transfer Mode (“ATM”) and Frame Relay are unreliable connection-oriented protocols. Connection-oriented protocols are in contrast to packet-oriented protocols such as UDP that transmit packets without a guaranteed ordering.

In embodiments utilizing a web server, the web server can run any of a variety of server or mid-tier applications, including Hypertext Transfer Protocol (“HTTP”) servers, FTP servers, Common Gateway Interface (“CGI”) servers, data servers, Java servers, Apache servers, and business application servers. The server(s) also may be capable of executing programs or scripts in response to requests from user devices, such as by executing one or more web applications that may be implemented as one or more scripts or programs written in any programming language, such as Java C, C#, or C++, or any scripting language, such as Ruby, PHP, Perl, Python, or TCL, as well as combinations thereof. The server(s) may also include database servers, including without limitation those commercially available from Oracle®, Microsoft®, Sybase®, and IBM® as well as open-source servers such as MySQL, Postgres, SQLite, MongoDB, and any other server capable of storing, retrieving, and accessing structured or unstructured data. Database servers may include table-based servers, document-based servers, unstructured servers, relational servers, non-relational servers, or combinations of these and/or other database servers.

The environment can include a variety of data stores and other memory and storage media as discussed above. These can reside in a variety of locations, such as on a storage medium local to (and/or resident in) one or more of the computers or remote from any or all of the computers across the network. In a particular set of embodiments, the information may reside in a storage-area network (“SAN”) familiar to those skilled in the art. Similarly, any necessary files for performing the functions attributed to the computers, servers or other network devices may be stored locally and/or remotely, as appropriate. Where a system includes computerized devices, each such device can include hardware elements that may be electrically coupled via a bus, the elements including, for example, at least one central processing unit (“CPU” or “processor”), at least one input device (e.g., a mouse, keyboard, controller, touch screen, or keypad), and at least one output device (e.g., a display device, printer, or speaker). Such a system may also include one or more storage devices, such as disk drives, optical storage devices, and solid-state storage devices such as random access memory (“RAM”) or read-only memory (“ROM”), as well as removable media devices, memory cards, flash cards, etc.

Such devices also can include a computer-readable storage media reader, a communications device (e.g., a modem, a network card (wireless or wired), an infrared communication device, etc.), and working memory as described above. The computer-readable storage media reader can be connected with, or configured to receive, a computer-readable storage medium, representing remote, local, fixed, and/or removable storage devices as well as storage media for temporarily and/or more permanently containing, storing, transmitting, and retrieving computer-readable information. The system and various devices also typically will include a number of software applications, modules, services, or other elements located within at least one working memory device, including an operating system and application programs, such as a client application or web browser. In addition, customized hardware might also be used and/or particular elements might be implemented in hardware, software (including portable software, such as applets), or both. Further, connection to other computing devices such as network input/output devices may be employed.

Storage media and computer readable media for containing code, or portions of code, can include any appropriate media known or used in the art, including storage media and communication media, such as, but not limited to, volatile and non-volatile, removable and non-removable media implemented in any method or technology for storage and/or transmission of information such as computer readable instructions, data structures, program modules, or other data, including RAM, ROM, Electrically Erasable Programmable Read-Only Memory (“EEPROM”), flash memory, or other memory technology, Compact Disc Read-Only Memory (“CD-ROM”), digital versatile disk (DVD), or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage, or other magnetic storage devices or any other medium which can be used to store the desired information and which can be accessed by the system device. Based on the disclosure and teachings provided herein, a person of ordinary skill in the art will appreciate other ways and/or methods to implement the various embodiments.

Example cryptographic algorithms include block ciphers and the various modes that utilize initialization vectors, such as the cipher-block chaining (CBC) mode, propagating cipher-block chaining (PCBC) mode, cipher feedback mode (CFB), output feedback (OFB) mode, counter (CTR) mode, and other modes, such as authenticated encryption modes such as eXtended Ciphertext Block Chaining (XCBC) mode, Integrity Aware CBC (IACBC) mode, Integrity Aware Parallelizable (IAPM) mode, Offset Codebook (OCB) mode, EAX and EAX Prime modes, Carter-Wegman+CTR (CWC) mode, Counter with CBC-MAC (CCM) mode, and Galois/Counter (GCM) mode.

As discussed, numerous variations utilize symmetric and/or asymmetric cryptographic primitives. Symmetric key algorithms may include various schemes for performing cryptographic operations on data including block ciphers, stream ciphers, and digital signature schemes. Example symmetric key algorithms include the advanced encryption standard (AES), the data encryption standard (DES), triple DES (3DES), Serpent, Twofish, blowfish, CASTS, RC4, and the international data encryption algorithm (IDEA). Symmetric key algorithms may also include those used to generate output of one way functions and include algorithms that utilize hash-based message authentication codes (HMACs), message authentication codes (MACs) in general, PBKDF2 and Bcrypt. Asymmetric key algorithms may also include various schemes for performing cryptographic operations on data. Example algorithms include those that utilize the Diffie-Hellman key exchange protocol, the digital signature standard (DSS), the digital signature algorithm, the ElGamal algorithm, various elliptic curve algorithms, password-authenticated key agreement techniques, the pallier cryptosystem, the RSA encryption algorithm (PKCS #1), the Cramer-Shoup cryptosystem, the YAK authenticated key agreement protocol, the NTRUEncrypt cryptosystem, the McEliece cryptosystem, and others. Elliptic curve algorithms include the elliptic curve Diffie-Hellman (ECDH) key agreement scheme, the Elliptic Curve Integrated Encryption Scheme (ECIES), the Elliptic Curve Digital Signature Algorithm (ECDSA), the ECMQV key agreement scheme, and the ECQV implicit certificate scheme. Other algorithms and combinations of algorithms are also considered as being within the scope of the present disclosure and the above is not intended to be an exhaustive list.

Note that the term “digital signature” includes any information usable to cryptographically verify authenticity of a message including information generated using an RSA-based digital scheme (such as RSA-PSS), the digital signature algorithm (DSA), and the elliptic curve digital signature algorithm, the ElGamal signature scheme, the Schnorr signature scheme, the Pointcheval-Stern signature algorithm, the Rabin signature algorithm, pairing-based digital signature schemes (such as the Boneh-Lynn-Schacham signature scheme), undeniable digital signature schemes, and others. Further, message authentication codes (such as hash-based message authentication codes (HMACs), keyed cryptographic hash functions, and other types of information may also be used as digital signatures.

It should be noted that the phrase “one-way function” includes functions that are not necessarily one-way in the strict mathematical sense, but that exhibit properties (such as collision resistance, preimage resistance and second preimage resistance) that render the function useful in contexts in which the various techniques of the present disclosure are applied. In this manner, an entity with output of the function but without access to the corresponding input, is unable to determine the input without, for instance, extraordinary expenditure of computational resources necessary for a cryptographic (e.g., brute force) attack. One-way functions (also referred to as “effectively one-way functions”) include, but are not limited to, cryptographic hash functions such as message authentication codes, (e.g., hash based message authentication code (HMAC)), key derivation functions, such as PBKDF2 and bcrypt (with the password being based at least in part on the plaintext and the cryptographic key, e.g.) and other secure randomization functions which may, but do not necessarily, have a domain (set of possible inputs) that is larger than their range (possible outputs). Other suitable functions (referred to as “f”) for various embodiments include, but are not limited to, functions that take at least a plaintext and cryptographic key as input and that have a property of preimage resistance (given a value y, the probability of randomly generating an input x such that f(x)=y is below a specified threshold), second preimage resistance (given an input x1, the probably of randomly generating another input x2, different from x1, such that f(x1)=f(x2) is below a specified threshold) and/or collision resistance (the probability of two different inputs resulting in the same output is less than a specified threshold). The exact threshold for each probability may be context-dependent, with lower probabilities corresponding to higher security contexts. Hash functions usable as one-way functions in accordance with the techniques of the present disclosure include, but are not limited to, functions described in the National Institute of Standards and Technology (NIST) Special Publication 800-107, Revision 1 “Recommendation for Applications Using Approved Hash Algorithms,” which is incorporated herein by reference.

Note that a system is said to be configured to trust a public cryptographic key if logic with which the system is configured to operate is dependent on whether an attempt to verify a digital signature with the public cryptographic key is successful. Similarly, a system is said to be configured to trust a symmetric cryptographic key if logic with which the system is configured to operate is dependent on whether an attempt to verify a digital signature with the symmetric cryptographic key is successful.

In various embodiments, data objects such as digital signatures may be cryptographically verifiable. In one example, cryptographically verifiable data objects are created to be cryptographically verifiable by the system to which the data object is to be provided or another system that operates in conjunction with the system to which the data object is to be provided. For example, the data object may be encrypted so as to be decryptable by the system that will cryptographically verify the data object, where the ability to decrypt the data object serves as cryptographic verification of the data object. As another example, the data object may be digitally signed (thereby producing a digital signature of the data object) such that the digital signature is verifiable by the system that will cryptographically verify the data object. In other examples, both encryption and digital signatures are used for cryptographic verifiability and/or security. The key used to encrypt and/or digitally sign the data object may vary in accordance with various embodiments and the same key is not necessarily used for both encryption and digital signing, where applicable. In some embodiments, a key used to encrypt the data object is a public key of a public/private key pair where the private key of the key pair is maintained securely by the system to which the data object is to be provided, thereby enabling the system to decrypt the data object using the private key of the key pair. Using the public key to encrypt the data object may include generating a symmetric key, using the symmetric key to encrypt the data object, and encrypting the symmetric key using the public key, where the encrypted symmetric key is provided to a system with the encrypted data object to enable the system to use the corresponding private key to decrypt the symmetric key and use the decrypted symmetric key to decrypt the data object. Further, in some embodiments, the data object is digitally signed using a private key of a public/private key pair corresponding to the computer system that encrypts and/or digitally signs the data object (e.g., a user device). For example, an application may be provisioned with the private key and the data object may include a certificate for the private key for use by a system for verification of the digital signature of the data object. Other variations, including variations where a symmetric key shared between the user computer and the system that cryptographically verifies the data object can be used to encrypt and/or digitally sign the data object.

In the preceding and following description, various techniques are described. For purposes of explanation, specific configurations and details are set forth in order to provide a thorough understanding of possible ways of implementing the techniques. However, it will also be apparent that the techniques described below may be practiced in different configurations without the specific details. Furthermore, well-known features may be omitted or simplified to avoid obscuring the techniques being described.

The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. It will, however, be evident that various modifications and changes may be made thereunto without departing from the broader spirit and scope of the invention as set forth in the claims.

Other variations are within the spirit of the present disclosure. Thus, while the disclosed techniques are susceptible to various modifications and alternative constructions, certain illustrated embodiments thereof are shown in the drawings and have been described above in detail. It should be understood, however, that there is no intention to limit the invention to the specific form or forms disclosed, but on the contrary, the intention is to cover all modifications, alternative constructions, and equivalents falling within the spirit and scope of the invention, as defined in the appended claims.

The use of the terms “a” and “an” and “the” and similar referents in the context of describing the disclosed embodiments (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. The term “connected,” when unmodified and referring to physical connections, is to be construed as partly or wholly contained within, attached to, or joined together, even if there is something intervening. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein and each separate value is incorporated into the specification as if it were individually recited herein. The use of the term “set” (e.g., “a set of items”) or “subset” unless otherwise noted or contradicted by context, is to be construed as a nonempty collection comprising one or more members. Further, unless otherwise noted or contradicted by context, the term “subset” of a corresponding set does not necessarily denote a proper subset of the corresponding set, but the subset and the corresponding set may be equal.

Conjunctive language, such as phrases of the form “at least one of A, B, and C,” or “at least one of A, B and C,” unless specifically stated otherwise or otherwise clearly contradicted by context, is otherwise understood with the context as used in general to present that an item, term, etc., may be either A or B or C, or any nonempty subset of the set of A and B and C. For instance, in the illustrative example of a set having three members, the conjunctive phrases “at least one of A, B, and C” and “at least one of A, B and C” refer to any of the following sets: {A}, {B}, {C}, {A, B}, {A, C}, {B, C}, {A, B, C}. Thus, such conjunctive language is not generally intended to imply that certain embodiments require at least one of A, at least one of B and at least one of C each to be present.

Operations of processes described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. Processes described herein (or variations and/or combinations thereof) may be performed under the control of one or more computer systems configured with executable instructions and may be implemented as code (e.g., executable instructions, one or more computer programs or one or more applications) executing collectively on one or more processors, by hardware or combinations thereof. The code may be stored on a computer-readable storage medium, for example, in the form of a computer program comprising a plurality of instructions executable by one or more processors. The computer-readable storage medium may be non-transitory. In some embodiments, the code is stored on set of one or more non-transitory computer-readable storage media having stored thereon executable instructions that, when executed (i.e., as a result of being executed) by one or more processors of a computer system, cause the computer system to perform operations described herein. The set of non-transitory computer-readable storage media may comprise multiple non-transitory computer-readable storage media and one or more of individual non-transitory storage media of the multiple non-transitory computer-readable storage media may lack all of the code while the multiple non-transitory computer-readable storage media collectively store all of the code. Further, in some examples, the executable instructions are executed such that different instructions are executed by different processors. As an illustrative example, a non-transitory computer-readable storage medium may store instructions. A main CPU may execute some of the instructions and a graphics processor unit may execute other of the instructions. Generally, different components of a computer system may have separate processors and different processors may execute different subsets of the instructions.

Accordingly, in some examples, computer systems are configured to implement one or more services that singly or collectively perform operations of processes described herein. Such computer systems may, for instance, be configured with applicable hardware and/or software that enable the performance of the operations. Further, computer systems that implement various embodiments of the present disclosure may, in some examples, be single devices and, in other examples, be distributed computer systems comprising multiple devices that operate differently such that the distributed computer system performs the operations described herein and such that a single device may not perform all operations.

The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate embodiments of the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention.

Embodiments of this disclosure are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate and the inventors intend for embodiments of the present disclosure to be practiced otherwise than as specifically described herein. Accordingly, the scope of the present disclosure includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the scope of the present disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 

What is claimed is:
 1. A computer-implemented method, comprising: acquiring a digital signature of a message; identifying a cryptographic key used to generate the digital signature; requesting, from a signature authority, proof that the cryptographic key is valid; receiving, from a key revocation service that is delegated authority to revoke the cryptographic key by the signature authority, a revocation value and an indication that the cryptographic key is revoked; cryptographically deriving a verification hash from a combination of a cryptographic hash of the revocation value and a cryptographic hash of a public portion of the cryptographic key; and confirming that the cryptographic key is revoked by verifying the verification hash against a public key of the signature authority that generated the cryptographic key using a hash tree generated under authority of the signature authority.
 2. The computer-implemented method of claim 1, wherein: the hash tree is generated from a set of hashes generated from a set of cryptographic keys that include the cryptographic key; and a root of the hash tree is the public key of the signature authority.
 3. The computer-implemented method of claim 1, wherein the key revocation service is provided by the signature authority.
 4. The computer-implemented method of claim 2, wherein: the combination of the cryptographic hash of the revocation value and the cryptographic hash of the public portion of the cryptographic key is further combined with at least one additional node of the hash tree; the verification hash is associated with a non-leaf node of the hash tree; and the revocation value proves the revocation of a plurality of cryptographic keys of the set of cryptographic keys.
 5. A system, comprising: at least one computing device coupled to a processor and a memory containing instructions that, as a result of being executed, implement one or more services that: acquire a digital signature; identify a cryptographic key used to generate the digital signature; request, from a signature authority, proof that the cryptographic key is valid; receive, from the signature authority, a revocation value and an indication that the cryptographic key is revoked; cryptographically derive a verification hash based on the revocation value and a public portion of the cryptographic key; and confirm that the cryptographic key is revoked by verifying the verification hash against a public key of the signature authority that generated the cryptographic key.
 6. The system of claim 5, wherein cryptographically deriving the verification hash is based on the combination of a cryptographic hash of the revocation value and a cryptographic hash of the public portion of the cryptographic key.
 7. The system of claim 6, wherein: the verification hash is a hash within a hash tree generated by the signature authority; the hash tree is generated based on a set of cryptographic keys that include the cryptographic key; and a root of the hash tree is the public key of the signature authority.
 8. The system of claim 7, wherein: the combination of the cryptographic hash of the revocation value and the cryptographic hash of the public portion of the cryptographic key is further combined with at least one additional node of the hash tree; and the revocation value proves the revocation of only one cryptographic key of the set of cryptographic keys.
 9. The system of claim 5, wherein the one or more services further: request, from a confirmation authority, proof that the cryptographic key is revoked; receive, from the confirmation authority, a confirmation value; generate a confirmation hash by determining a hash of a combination of the cryptographic hash of the revocation value and the cryptographic hash of the public portion of the cryptographic key and a cryptographic hash of the confirmation value; and confirm that the cryptographic key is revoked by verifying the confirmation hash against the public key of the signature authority that generated the cryptographic key.
 10. The system of claim 5, wherein the one or more services further: request, from a confirmation authority, proof that the cryptographic key is not revoked; receive, from the confirmation authority, a confirmation value; generate a confirmation hash by determining a hash of a combination of the cryptographic hash of the revocation value and the cryptographic hash of the public portion of the cryptographic key and a cryptographic hash of the confirmation value; and confirm that the cryptographic key has not been revoked by verifying the confirmation hash against the public key of the signature authority that generated the cryptographic key.
 11. The system of claim 9, wherein the one or more services further: as a result of receiving the indication that the cryptographic key is revoked, receive a new cryptographic key from the signature authority; and generate a new digital signature based on the new cryptographic key.
 12. The system of claim 5, wherein the one or more services further: receive the cryptographic key from the signature authority; and generate the digital signature using the cryptographic key.
 13. A non-transitory computer-readable storage medium having stored thereon executable instructions that, as a result of being executed by one or more processors of at least one computer system, cause the computer system to at least: acquire a digital signature associated with a message; identify a cryptographic key used to generate the digital signature; request, from a signature authority, proof that the cryptographic key is valid; receive, from the signature authority, a revocation value and an indication that the cryptographic key is revoked; cryptographically derive a verification hash from a combination of a cryptographic hash of the revocation value and a cryptographic hash of a public portion of the cryptographic key; and confirm that the cryptographic key is revoked by verifying the verification hash against a public key of the signature authority that generated the cryptographic key.
 14. The non-transitory computer-readable storage medium of claim 13, wherein: the verification hash is a hash within a hash tree generated by the signature authority; the hash tree is generated from a set of hashes generated from a set of cryptographic keys that include the cryptographic key; and a root of the hash tree is the public key of the signature authority.
 15. The non-transitory computer-readable storage medium of claim 14, wherein: the combination of the cryptographic hash of the revocation value and the cryptographic hash of the public portion of the cryptographic key is further combined with at least one additional node of the hash tree; the verification hash is associated with a non-leaf node of the hash tree; and the revocation value proves the revocation of a plurality of cryptographic keys of the set of cryptographic keys.
 16. The non-transitory computer-readable storage medium of claim 13, wherein the instructions further comprise instructions that, as a result of being executed by the one or more processors, cause the computer system to: request, from a confirmation authority, proof that the cryptographic key is revoked; receive, from the confirmation authority, a confirmation value; generate a confirmation hash by determining a hash of a combination of the cryptographic hash of the revocation value and the cryptographic hash of the public portion of the cryptographic key and a cryptographic hash of the confirmation value; and confirm that the cryptographic key is revoked by verifying the confirmation hash against the public key of the signature authority that generated the cryptographic key.
 17. The non-transitory computer-readable storage medium of claim 13, wherein the instructions further comprise instructions that, as a result of being executed by the one or more processors, cause the computer system to: request, from a confirmation authority, proof that the cryptographic key is not revoked; receive, from the confirmation authority, a confirmation value; generate a confirmation hash by determining a hash of a combination of the cryptographic hash of the revocation value and the cryptographic hash of the public portion of the cryptographic key and a cryptographic hash of the confirmation value; and confirm that revocation of the cryptographic key is rescinded by verifying the confirmation hash against the public key of the signature authority that generated the cryptographic key.
 18. The non-transitory computer-readable storage medium of claim 13, wherein the instructions further comprise instructions that, as a result of being executed by the one or more processors, cause the computer system to: as a result of receiving the indication that the cryptographic key is revoked, receive a new cryptographic key from the signature authority; and generate a new digital signature for the message.
 19. The non-transitory computer-readable storage medium of claim 13, wherein the instructions further comprise instructions that, as a result of being executed by the one or more processors, cause the computer system to: receive the cryptographic key from the signature authority; and generate a digital signature of the message using the cryptographic key.
 20. The non-transitory computer-readable storage medium of claim 13, wherein: the signature authority is a service running on a remote computer system; a request for proof that the cryptographic key is valid is submitted to the service running on the remote computer system via a network service interface; and the revocation value is received as a response to the request via the network service interface. 